test(bigtable): remove unnecessary deep stubs from streaming callable mocks

Remove `defaultAnswer(Answers.RETURNS_DEEP_STUBS)` from programmatic
mocks of `ServerStreamingCallable` in `BigtableDataClientTests`.
Mockito's deep stubs cause reflection crashes on Java 8 when dealing
with JSpecify annotations. Since the tests do not rely on deep stubs
for these callables, they can be safely removed.

TAG=agy
CONV=de3ef09d-a26c-4190-b578-4c993f807bdc

Author: lqiu96

java-bigtable/google-cloud-bigtable/src/test/java/com/google/cloud/bigtable/data/v2/BigtableDataClientTests.java

@@ -105,9 +105,7 @@ public void setUp() {
     mockStub =
         Mockito.mock(EnhancedBigtableStub.class, Mockito.withSettings().withoutAnnotations());
     mockReadRowsCallable =
-        Mockito.mock(
-            ServerStreamingCallable.class,
-            Mockito.withSettings().withoutAnnotations().defaultAnswer(Answers.RETURNS_DEEP_STUBS));
+        Mockito.mock(ServerStreamingCallable.class, Mockito.withSettings().withoutAnnotations());
     mockReadRowCallable =
         Mockito.mock(UnaryCallable.class, Mockito.withSettings().withoutAnnotations());
     mockSampleRowKeysCallable =
@@ -129,13 +127,9 @@ public void setUp() {
     mockPrepareQueryCallable =
         Mockito.mock(UnaryCallable.class, Mockito.withSettings().withoutAnnotations());
     mockGenerateInitialChangeStreamPartitionsCallable =
-        Mockito.mock(
-            ServerStreamingCallable.class,
-            Mockito.withSettings().withoutAnnotations().defaultAnswer(Answers.RETURNS_DEEP_STUBS));
+        Mockito.mock(ServerStreamingCallable.class, Mockito.withSettings().withoutAnnotations());
     mockReadChangeStreamCallable =
-        Mockito.mock(
-            ServerStreamingCallable.class,
-            Mockito.withSettings().withoutAnnotations().defaultAnswer(Answers.RETURNS_DEEP_STUBS));
+        Mockito.mock(ServerStreamingCallable.class, Mockito.withSettings().withoutAnnotations());
 
     bigtableDataClient = new BigtableDataClient(mockStub);
   }