Many of these are tests, false positives (e.g. base64 images or "Migration1599570560FixSlovakiaDisplayedAsSloveniaTest"), or examples from documentation.
Can't find a single match for an actual API key.
Can't find a single match for an actual API key.
https://grep.app/search?current=2&q=api_key%20%3D%20%22%5Ba-...
As others have posted, Github implemented an alerting system for keys/passwords/etc. that have been checked into the codebase. My guess is most of these will be invalidated by now, either by the developer requesting a new key (and not publishing it), or the provider invalidating it for them.