Fix the issues reported by phpcs

phpcs --standard=DrupalPractice shows the following report.

FILE: tests/src/Functional/FontYourFaceInstallTest.php
------------------------------------------------------
FOUND 0 ERRORS AND 5 WARNINGS AFFECTING 5 LINES
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 54 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
 58 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
 62 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
 66 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
 67 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
-------------------------------------------------------


FILE: tests/src/Functional/FontYourFaceSubmoduleInstallTest.php
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FOUND 0 ERRORS AND 3 WARNINGS AFFECTING 3 LINES
-------------------------------------------------------
 52 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
 53 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
 67 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
-------------------------------------------------------

FILE: tests/src/Functional/FontYourFaceLocalFontInstallTest.php
-------------------------------------------------------
FOUND 0 ERRORS AND 2 WARNINGS AFFECTING 2 LINES
-------------------------------------------------------
 52 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
 54 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()
    |         | instead
-------------------------------------------------------


FILE: modules/local_fonts/src/Form/LocalFontConfigEntityForm.php
---------------------------------------
FOUND 0 ERRORS AND 3 WARNINGS AFFECTING 3 LINES
---------------------------------------
 131 | WARNING | File::load calls should be avoided in classes, use dependency injection instead
 139 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 145 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
---------------------------------------


FILE: src/Form/FontForm.php
----------------
FOUND 0 ERRORS AND 3 WARNINGS AFFECTING 3 LINES
----------------
 21 | WARNING | Unused variable $entity.
 35 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 41 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
----------------


FILE: src/Form/FontDisplayForm.php
-----------------
FOUND 0 ERRORS AND 4 WARNINGS AFFECTING 4 LINES
-----------------
  46 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  56 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 173 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 179 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
-----------------


FILE: src/Form/FontSettingsForm.php
-----------------
FOUND 0 ERRORS AND 5 WARNINGS AFFECTING 5 LINES
-----------------
  57 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  83 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  86 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 123 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 138 | WARNING | Unused variable $config.
-----------------


FILE: src/Controller/FontYourFaceController.php
----------------------
FOUND 0 ERRORS AND 6 WARNINGS AFFECTING 6 LINES
----------------------
  28 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  45 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  58 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  75 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  92 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 105 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
----------------------


FILE: src/Plugin/views/filter/FontYourFaceStyleFilter.php
--------------------------------
FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
--------------------------------
 55 | WARNING | Unused variable $exposed.
--------------------------------


FILE: src/Plugin/views/filter/FontYourFaceProviderFilter.php
-----------------------------------
FOUND 0 ERRORS AND 3 WARNINGS AFFECTING 3 LINES
-----------------------------------
 44 | WARNING | Unused variable $name.
 47 | WARNING | Unused variable $name.
 59 | WARNING | Unused variable $exposed.
-----------------------------------


FILE: src/Plugin/views/filter/FontYourFaceWeightFilter.php
---------------------------------
FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
---------------------------------
 62 | WARNING | Unused variable $exposed.
---------------------------------

Those files need to be changed to fix the reported issues