Strategy: Improve curl error message finding

[samford]

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When I originally migrated livecheck to curl, the errors we were encountering typically started with curl: and a number in parentheses before the error message (e.g., curl: (60) SSL certificate problem: certificate has expired). However, curl produces some errors that don't adhere to this format.

In some cases, the error message doesn't include a leading number in parentheses. Additionally, some errors can include multiple messages. For example:

curl: option --something: is unknown
curl: try 'curl --help' or 'curl --manual' for more information

With this in mind, it's necessary to loosen the regex that's used to identify curl error messages and to use #scan to collect all of the error message lines in stderr. Otherwise we incorrectly miss certain error messages and get the fallback cURL failed without an error message, which we shouldn't see.

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For what it's worth, I encountered this shortcoming as part of implementing support for specifying curl args in a livecheck block. I'll be creating a PR for that work soon but I wanted to extract this commit from that branch beforehand, to simplify the forthcoming PR.

[BrewTestBot]

Review period will end on 2021-09-07 at 00:00:00 UTC.

[MikeMcQuaid]

Makes sense! One wording tweak to avoid this happening again if the format doesn't align again in future.

[BrewTestBot]

Review period ended.