isort 5 compatibility (#7786)

The CI appears to use the latest version of isort, which is a problem when isort gets a major version bump. Rather than try to pin the version, I've done the necessary to make isort5 happy with synapse.

scripts-dev/check_signature.py

@@ -2,9 +2,9 @@ import argparse
 import json
 import logging
 import sys
-import urllib2
 
 import dns.resolver
+import urllib2
 from signedjson.key import decode_verify_key_bytes, write_signing_keys
 from signedjson.sign import verify_signed_json
 from unpaddedbase64 import decode_base64

scripts-dev/lint.sh

@@ -15,7 +15,7 @@ else
 fi
 
 echo "Linting these locations: $files"
-isort -y -rc $files
+isort $files
 python3 -m black $files
 ./scripts-dev/config-lint.sh
 flake8 $files