test: Disable copying annotation on mocks for Java 8 CIs

[nnicolee]

In JSpecify 1.0.0, the @NullMarked annotation includes ElementType.MODULE in its @Target metadata. Because ElementType.MODULE was introduced in Java 9, reflecting on @NullMarked classes under Java 8 (JDK 1.8) throws EnumConstantNotPresentExceptionProxy wrapped in an ArrayStoreException.

When unit tests run on Java 8, Mockito's default mock generation (via ByteBuddy) attempts to copy all runtime class annotations from target classes onto mock subclasses. This triggers the reflection crash when mocking generated stub and settings classes that are annotated with @NullMarked.

To bypass this Java 8 limitation:

• Replaced default Mockito mock instantiation with Mockito.mock(Class, Mockito.withSettings().withoutAnnotations()) across the failing unit test suites.
• Disabling annotation copying prevents Mockito/ByteBuddy from invoking Class.getAnnotations() on the target class during proxy creation, allowing tests to run and mock stubs successfully on Java 8 pipelines.

Modified Mockito mock setups in:

• StreamingSubscriberConnectionTest
• SpannerImplTest
• SpannerCloudMonitoringExporterTest
• BigtableInstanceAdminClientV2Test
• BigtableTableAdminClientV2Test
• BigtableCloudMonitoringExporterTest
• GrpcLongRunningClientTest

[gemini-code-assist]

Code Review

This pull request refactors several test classes across different modules to instantiate Mockito mocks explicitly using withSettings().withoutAnnotations() instead of using @Mock annotations or standard mock() calls. The feedback suggests removing the now-unused mockitoRule fields and their associated imports in SpannerCloudMonitoringExporterTest and BigtableTableAdminClientV2Test since no @Mock annotations remain in those classes.

[lqiu96]

LGTM for GAX

[sonarqubecloud]

Quality Gate passed for 'gapic-generator-java-root'

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

[sonarqubecloud]

Quality Gate passed for 'gapic-generator-java-root'

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