fix: Display a warning (instead of exiting early) when unable to find recent issues on a tap

[boblail]

Occasionally, when failing to brew install or brew upgrade a formula, users will get an error message and the last line of it will be:

Error: Validation Failed: [{"message"=>"The listed users and repositories cannot be searched either because the resources do not exist or you do not have permission to view them.", "resource"=>"Search", "field"=>"q", "code"=>"invalid"}]

Here's an old public example: https://gitlab.com/tabos/rogerrouter/-/issues/21

At Square, this error can be caused by a transient issue with a user's GitHub credentials.

My proposal is that any error which prevents brew from showing related issues should:

1. Not cause brew to exit early (vs. printing diagnostic checks and doing any other cleanup)
2. Be clearly differentiated from the original failure (so it doesn't become a red herring for users troubleshooting their broken formula)

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[MikeMcQuaid]

Thanks again @boblail!

[boblail]

Thanks all!