Update moto requirement

There was a regression in moto 5.0.3 that broke the S3 tests, so require the version that includes the fix.

Author: dhirving

requirements.txt

@@ -5,7 +5,8 @@ importlib_resources
 backoff >= 1.10
 boto3 >= 1.13
 botocore >= 1.15
-moto >= 1.3,!=5.0.0
+# A moto regression that breaks our tests is fixed in 5.0.4
+moto >= 4, != 5.0.0, != 5.0.1, != 5.0.2, != 5.0.3
 responses >= 0.12.0
 urllib3 >= 1.25.10
 requests >= 2.26.0