test(spanner): clear context-aware mTLS env var in unit tests

Unset CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE in mTLS unit tests to prevent failures in Google and Kokoro CI environments.

Author: sakthivelmanii

packages/gapic-generator/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2

@@ -896,6 +896,7 @@ def test_{{ service.client_name|snake_case }}_get_mtls_endpoint_and_cert_source(
         for config_data, expected_cert_source in test_cases:
             env = os.environ.copy()
             env.pop("GOOGLE_API_USE_CLIENT_CERTIFICATE", None)
+            env.pop("CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE", None)
             with mock.patch.dict(os.environ, env, clear=True):
                     config_filename = "mock_certificate_config.json"
                     config_file_content = json.dumps(config_data)
@@ -943,6 +944,7 @@ def test_{{ service.client_name|snake_case }}_get_mtls_endpoint_and_cert_source(
         for config_data, expected_cert_source in test_cases:
             env = os.environ.copy()
             env.pop("GOOGLE_API_USE_CLIENT_CERTIFICATE", "")
+            env.pop("CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE", "")
             with mock.patch.dict(os.environ, env, clear=True):
                     config_filename = "mock_certificate_config.json"
                     config_file_content = json.dumps(config_data)
@@ -963,13 +965,25 @@ def test_{{ service.client_name|snake_case }}_get_mtls_endpoint_and_cert_source(
                             assert cert_source is expected_cert_source
 
     # Test the case GOOGLE_API_USE_MTLS_ENDPOINT is "never".
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "never"}):
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_MTLS_ENDPOINT": "never",
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
         api_endpoint, cert_source = client_class.get_mtls_endpoint_and_cert_source()
         assert api_endpoint == client_class.DEFAULT_ENDPOINT
         assert cert_source is None
 
     # Test the case GOOGLE_API_USE_MTLS_ENDPOINT is "always".
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "always"}):
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_MTLS_ENDPOINT": "always",
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
         api_endpoint, cert_source = client_class.get_mtls_endpoint_and_cert_source()
         assert api_endpoint == client_class.DEFAULT_MTLS_ENDPOINT
         assert cert_source is None