IBX-12606: Migrated the test suites to PHPUnit 11

[ViniTou]

🎫 Issue	IBX-12606
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Description:

• Migrated the test suites from PHPUnit 9 to PHPUnit 11 (phpunit/phpunit ^11.5, matthiasnoback/symfony-dependency-injection-test ^6.0).
• Migrated phpunit.xml.dist and phpunit.integration.xml.dist to the 11.5 schema (dropped removed config attributes, added cacheDirectory).
• Converted @dataProvider/@covers annotations to #[DataProvider]/#[CoversClass] attributes and made data providers static.
• Replaced createMock() with createStub() where no expectations are set on the double, and renamed getInvocationCount() to numberOfInvocations().
• Renamed the abstract test base classes BaseMapperTest/AbstractGroupedContentFormFieldsProviderTest to *TestCase (PHPUnit 11 warns/fails on concrete-looking *Test classes that are abstract) and updated their consumers and the PHPStan baseline accordingly.
• Added .phpunit.cache/ to .gitignore.

For QA:

N/A

Documentation:

N/A

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud