Fix OAuth2 client tests for Python 3.12 and newer.
Replace the deprecated and removed unittest.assertRaisesRegexp()
alias with assertRaisesRegex() to maintain compatibility with
modern Python versions while preserving exception message checks.
--- ../tests/test_client.py	2026-10-16 17:26:52.613040988 +0300
+++ ../tests/test_client.py	2026-10-16 17:27:55.542702028 +0300
@@ -436,7 +436,7 @@
             'File {0} \(pointed by {1} environment variable\) does not '
             'exist!'.format(
                 nonexistent_file, client.GOOGLE_APPLICATION_CREDENTIALS))
-        with self.assertRaisesRegexp(client.ApplicationDefaultCredentialsError,
+        with self.assertRaisesRegex(client.ApplicationDefaultCredentialsError,
                                      expected_err_msg):
             client._get_environment_variable_file()
 
@@ -541,7 +541,7 @@
             "'{1}' values\)".format(client.AUTHORIZED_USER,
                                     client.SERVICE_ACCOUNT))
 
-        with self.assertRaisesRegexp(client.ApplicationDefaultCredentialsError,
+        with self.assertRaisesRegex(client.ApplicationDefaultCredentialsError,
                                      expected_err_msg):
             client._get_application_default_credential_from_file(
                 credentials_file)
@@ -552,7 +552,7 @@
                          'application_default_credentials_malformed_2.json'))
         expected_err_msg = (
             'The following field\(s\) must be defined: private_key_id')
-        with self.assertRaisesRegexp(client.ApplicationDefaultCredentialsError,
+        with self.assertRaisesRegex(client.ApplicationDefaultCredentialsError,
                                      expected_err_msg):
             client._get_application_default_credential_from_file(
                 credentials_file)
@@ -569,7 +569,7 @@
         missing_fields = ['first', 'second', 'third']
         expected_err_msg = ('The following field\(s\) must be defined: ' +
                             ', '.join(missing_fields))
-        with self.assertRaisesRegexp(client.ApplicationDefaultCredentialsError,
+        with self.assertRaisesRegex(client.ApplicationDefaultCredentialsError,
                                      expected_err_msg):
             client._raise_exception_for_missing_fields(missing_fields)
 
@@ -580,7 +580,7 @@
         expected_err_msg = ('An error was encountered while reading '
                             'json file: ' + credential_file +
                             extra_help + ': ' + str(error))
-        with self.assertRaisesRegexp(client.ApplicationDefaultCredentialsError,
+        with self.assertRaisesRegex(client.ApplicationDefaultCredentialsError,
                                      expected_err_msg):
             client._raise_exception_for_reading_json(
                 credential_file, extra_help, error)
@@ -721,7 +721,7 @@
         credentials_filename = None
         expected_err_msg = (r'The parameter passed to the from_stream\(\) '
                             r'method should point to a file.')
-        with self.assertRaisesRegexp(client.ApplicationDefaultCredentialsError,
+        with self.assertRaisesRegex(client.ApplicationDefaultCredentialsError,
                                      expected_err_msg):
             self.get_a_google_credentials_object().from_stream(
                 credentials_filename)
@@ -737,7 +737,7 @@
             "'type' field should be defined \(and have one of the '" +
             client.AUTHORIZED_USER + "' or '" + client.SERVICE_ACCOUNT +
             "' values\)")
-        with self.assertRaisesRegexp(client.ApplicationDefaultCredentialsError,
+        with self.assertRaisesRegex(client.ApplicationDefaultCredentialsError,
                                      expected_err_msg):
             self.get_a_google_credentials_object().from_stream(
                 credentials_file)
@@ -752,7 +752,7 @@
             ' \(provided as parameter to the from_stream\(\) method\): '
             'The following field\(s\) must be defined: '
             'private_key_id')
-        with self.assertRaisesRegexp(client.ApplicationDefaultCredentialsError,
+        with self.assertRaisesRegex(client.ApplicationDefaultCredentialsError,
                                      expected_err_msg):
             self.get_a_google_credentials_object().from_stream(
                 credentials_file)
@@ -1872,7 +1872,7 @@
             data=b'error=invalid_request',
         )
 
-        with self.assertRaisesRegexp(client.FlowExchangeError,
+        with self.assertRaisesRegex(client.FlowExchangeError,
                                      'invalid_request'):
             self.flow.step2_exchange(code='some random code', http=http)
 
@@ -2055,7 +2055,7 @@
         http = http_mock.HttpMock(data=payload)
 
         code = {'error': 'thou shall not pass'}
-        with self.assertRaisesRegexp(
+        with self.assertRaisesRegex(
                 client.FlowExchangeError, 'shall not pass'):
             self.flow.step2_exchange(code=code, http=http)
 
@@ -2188,7 +2188,7 @@
 
         err_msg = ('This OAuth 2.0 flow is unsupported: '
                    '{0!r}'.format(client_type))
-        with self.assertRaisesRegexp(client.UnknownClientSecretsFlowError,
+        with self.assertRaisesRegex(client.UnknownClientSecretsFlowError,
                                      err_msg):
             client.flow_from_clientsecrets(filename, None, cache=cache)