Retry all > 400 errors on a list operation failing

Looking at the recent failures, this operation seemed to be a common cause.

I've followed the convention of >= 400 used elsewhere in the code, which should be safe given that this is a list rather than create or update operation.

Closes #25 (closed)

.gitignore

@@ -112,3 +112,5 @@ credentials.json
 
 # Local configuration
 gsuitesync.yaml
+
+.vscode/
\ No newline at end of file