\Drupal calls should be avoided in classes

Problem/Motivation

From https://git.drupalcode.org/project/webform_eloqua/-/jobs/1423413

$ php vendor/bin/phpstan analyze $_WEB_ROOT/modules/custom/$CI_PROJECT_NAME $PHPSTAN_CONFIGURATION --no-progress || EXIT_CODE=$?
 ------ ---------------------------------------------------------------------- 
  Line   src/Plugin/WebformHandler/WebformEloquaHandler.php                    
 ------ ---------------------------------------------------------------------- 
  291    \Drupal calls should be avoided in classes, use dependency injection  
         instead                                                               
  387    \Drupal calls should be avoided in classes, use dependency injection  
         instead                                                               
 ------ ---------------------------------------------------------------------- 
 [ERROR] Found 2 errors  

Steps to reproduce

Run Gitlab CI

Proposed resolution

Use dependency injection

Remaining tasks

1. Update the code
2. Test manually

User interface changes

None

API changes

None

Data model changes

None