[CodeQuality] Skip TestCase suffix classes in RemoveNeverUsedMockPropertyRector

[TomasVotruba]

Abstract *TestCase classes are most likely extended, with mock properties used in child test classes. This rule was removing those still-used mocks. Now skips any class whose name ends with TestCase.

-abstract class SomeAbstractTestCase extends TestCase
-{
-    private MockObject $mockProperty;
-
-    protected function setUp(): void
-    {
-        $this->mockProperty = $this->createMock(\stdClass::class);
-        $this->mockProperty->expects($this->once())
-            ->method('someMethod')
-            ->willReturn('someValue');
-    }
-}

Above class is now left untouched (skip_test_case_suffix.php.inc fixture).