Fix broken handling of certain calls in GitHub importer client

## What does this MR do?
It changes/fixes the behavior of request handling in GH client. Now it returns the response directly if it's not a collection of resources. Otherwise, it checks for a passed block, if true, then it yield each page to said block, if not, it collects all response in a single array then returns it.

Closes #22998

See merge request !6703