test(spanner): disable annotation copying on ServerStream mocks causing Java 8 crash

[nnicolee]

Problem

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

In PartitionedDmlTransactionTest, two mock declarations for ServerStream were created using the default mock(ServerStream.class) without setting .withoutAnnotations(). Mockito attempts to copy annotations on the mock subclasses, triggering the reflection crash on the JSpecify @NullMarked annotation during Java 8 CI pipelines.

Solution

Replaced mock(ServerStream.class) with mock(ServerStream.class, withSettings().withoutAnnotations()) in testExecuteStreamingPartitionedUpdateRSTstream and testExecuteStreamingPartitionedUpdateGenericInternalException to match the other passing tests. This disables annotation copying on the mocked ServerStream instances and bypasses the Java 8 reflection limitations.

[gemini-code-assist]

Code Review

This pull request updates PartitionedDmlTransactionTest.java to use withSettings().withoutAnnotations() when mocking ServerStream in three test cases. There are no review comments, so I have no feedback to provide.