Avoid clashing test mocks of QuantumEngineServiceClient

Restrict mocking to the relevant test module only.

Fixes quantumlib#5870.

Author: pavoljuhas

cirq-google/cirq_google/engine/engine_job_test.py

@@ -28,7 +28,7 @@
 from cirq_google.engine.test_utils import uses_async_mock
 
 
-@pytest.fixture(scope='session', autouse=True)
+@pytest.fixture(scope='module', autouse=True)
 def mock_grpc_client():
     with mock.patch(
         'cirq_google.engine.engine_client.quantum.QuantumEngineServiceClient'

cirq-google/cirq_google/engine/engine_processor_test.py

@@ -207,7 +207,7 @@ def _to_timestamp(json_string):
 )
 
 
-@pytest.fixture(scope='session', autouse=True)
+@pytest.fixture(scope='module', autouse=True)
 def mock_grpc_client():
     with mock.patch(
         'cirq_google.engine.engine_client.quantum.QuantumEngineServiceClient'

cirq-google/cirq_google/engine/engine_program_test.py

@@ -479,7 +479,7 @@ def test_get_batch_size(get_program_async):
         _ = program.batch_size()
 
 
-@pytest.fixture(scope='session', autouse=True)
+@pytest.fixture(scope='module', autouse=True)
 def mock_grpc_client():
     with mock.patch(
         'cirq_google.engine.engine_client.quantum.QuantumEngineServiceClient'

cirq-google/cirq_google/engine/engine_test.py

@@ -276,7 +276,7 @@ def test_make_random_id():
     assert random_id != random_id2
 
 
-@pytest.fixture(scope='session', autouse=True)
+@pytest.fixture(scope='module', autouse=True)
 def mock_grpc_client_async():
     with mock.patch(
         'cirq_google.engine.engine_client.quantum.QuantumEngineServiceAsyncClient', autospec=True