Address Deprecated Code in Tests; Coding Standards

Problem/Motivation

There are a number of deprecation notices being thrown by tests:

$ ../vendor/phpunit/phpunit/phpunit -c core/ modules/contrib/ckeditor_config/ --verbose
PHPUnit 9.5.5 by Sebastian Bergmann and contributors.

Runtime:       PHP 7.3.25-1+0~20201130.73+debian10~1.gbp042074
Configuration: /var/www/html/web/core/phpunit.xml.dist
Warning:       Your XML configuration validates against a deprecated schema.
Suggestion:    Migrate your XML configuration using "--migrate-configuration"!

Testing /var/www/html/web/modules/contrib/ckeditor_config
.                                                                   1 / 1 (100%)

Time: 00:50.458, Memory: 6.00 MB

OK (1 test, 17 assertions)

Remaining self deprecation notices (2)

  1x: Declaring ::setUp without a void return typehint in Drupal\Tests\ckeditor_config\FunctionalJavascript\CkeditorConfigTest is deprecated in drupal:9.0.0. Typehinting will be required before drupal:10.0.0. See https://www.drupal.org/node/3114724
    1x in DrupalListener::startTest from Drupal\Tests\Listeners

  1x: The Drupal\Tests\ckeditor_config\FunctionalJavascript\CkeditorConfigTest::$modules property must be declared protected. See https://www.drupal.org/node/2909426
    1x in DrupalListener::startTest from Drupal\Tests\Listeners

There is also a coding standing issues:

$ phpcs --standard=Drupal,DrupalPractice *

FILE: ...oembed-providers/web/modules/contrib/ckeditor_config/js/ckeditor_config.js
--------------------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
--------------------------------------------------------------------------------
 21 | ERROR | [x] Expected 1 newline at end of file; 0 found
--------------------------------------------------------------------------------
PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
--------------------------------------------------------------------------------

Time: 275ms; Memory: 10MB

This issue is targeted at 8.x-3.x as no further development is planned for 8.x-2.x.

Proposed resolution

Update code to address issues.

Remaining tasks

Submit patch.

User interface changes

None.

API changes

None.

Data model changes

None.