Issue #3279108 by phenaproxima: Merge package_manager_test_fixture into package_manager_bypass

automatic_updates_extensions/src/ExtensionUpdater.php

.../Validator/PackagesInstalledWithComposerValidatorTest.php

...ger/tests/modules/package_manager_bypass/src/Beginner.php

.../package_manager_bypass/src/BypassedStagerServiceBase.php

...er/tests/modules/package_manager_bypass/src/Committer.php

...anager_bypass/src/PackageManagerBypassServiceProvider.php

...nager/tests/modules/package_manager_bypass/src/Stager.php

...anager_test_fixture/package_manager_test_fixture.info.yml

...er_test_fixture/package_manager_test_fixture.services.yml

...anager_test_fixture/src/EventSubscriber/FixtureStager.php

package_manager/tests/src/Kernel/LockFileValidatorTest.php

...manager/tests/src/Kernel/PackageManagerKernelTestBase.php

...manager/tests/src/Kernel/PathExcluder/GitExcluderTest.php

package_manager/tests/src/Kernel/StageOwnershipTest.php

package_manager/tests/src/Kernel/StageTest.php

package_manager/tests/src/Kernel/SymlinkValidatorTest.php

...anager/tests/src/Traits/PackageManagerBypassTestTrait.php

tests/src/Functional/AvailableUpdatesReportTest.php

tests/src/Functional/ReadinessValidationTest.php

tests/src/Functional/UpdateLockTest.php