gax-java: Flaky BatcherImplTest.testThrottlingBlocking - Zero interactions with this mock

The below test failed and then passed on rerun.
```
Error:  Failures: 
Error:    BatcherImplTest.testThrottlingBlocking:897 
Wanted but not invoked:
apiCallContext.withOption(
    <Capturing argument>,
    <Capturing argument>
);
-> at com.google.api.gax.batching.BatcherImplTest.testThrottlingBlocking(BatcherImplTest.java:897)
Actually, there were zero interactions with this mock.
```