PYTHON-3210 Remove flakey string assertion from invalid aws creds FLE test (#922)

(cherry picked from commit 3cb16ca)

Author: ShaneHarvey

test/test_encryption.py

@@ -1211,9 +1211,9 @@ def test_05_aws_endpoint_wrong_region(self):
         }
         # The full error should be something like:
         # "Credential should be scoped to a valid region, not 'us-east-1'"
-        # but we only check for "us-east-1" to avoid breaking on slight
+        # but we only check for EncryptionError to avoid breaking on slight
         # changes to AWS' error message.
-        with self.assertRaisesRegex(EncryptionError, "us-east-1"):
+        with self.assertRaises(EncryptionError):
             self.client_encryption.create_data_key("aws", master_key=master_key)
 
     @unittest.skipUnless(any(AWS_CREDS.values()), "AWS environment credentials are not set")