refactor(phpstan): Fix PHPStan reports for test base class (#3104477)

coder_sniffer/Drupal/Test/Arrays/ArrayUnitTest.php

...er/Drupal/Test/Arrays/DisallowLongArraySyntaxUnitTest.php

...iffer/Drupal/Test/Classes/ClassCreateInstanceUnitTest.php

..._sniffer/Drupal/Test/Classes/ClassDeclarationUnitTest.php

coder_sniffer/Drupal/Test/Classes/ClassFileNameUnitTest.php

...r/Drupal/Test/Classes/FullyQualifiedNamespaceUnitTest.php

...iffer/Drupal/Test/Classes/PropertyDeclarationUnitTest.php

...niffer/Drupal/Test/Classes/UnusedUseStatementUnitTest.php

...iffer/Drupal/Test/Classes/UseLeadingBackslashUnitTest.php

coder_sniffer/Drupal/Test/CoderSniffUnitTest.php

...r_sniffer/Drupal/Test/Commenting/ClassCommentUnitTest.php

...ffer/Drupal/Test/Commenting/DataTypeNamespaceUnitTest.php

coder_sniffer/Drupal/Test/Commenting/DeprecatedUnitTest.php

...er/Drupal/Test/Commenting/DocCommentAlignmentUnitTest.php

...sniffer/Drupal/Test/Commenting/DocCommentStarUnitTest.php

coder_sniffer/Drupal/Test/Commenting/DocCommentUnitTest.php

coder_sniffer/Drupal/Test/Commenting/FileCommentUnitTest.php

...niffer/Drupal/Test/Commenting/FunctionCommentUnitTest.php

...r/Drupal/Test/Commenting/GenderNeutralCommentUnitTest.php

coder_sniffer/Drupal/Test/Commenting/HookCommentUnitTest.php