Strategy: Add --silent flag to DEFAULT_CURL_ARGS

[samford]

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This is a recreation of #12647, as I was encountering persistent CI failures that I didn't think were related to the committed changes (based on what I saw in testing). Digging into this further, it turned out that the failures were, in fact, due to the #curl_args commit where I used #uniq on the returned array. My intention was to avoid having options duplicated between args and extra_args (e.g., including --silent twice), simply for the sake of tidiness, but this approach causes problems because some options can be used more than once (e.g., --header).

Unfortunately, I modified the related branch, so I couldn't re-open the previous PR. That said, this PR is the same as the last one but I've dropped the #curl_args commit.

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Currently, only Livecheck::Strategy::PAGE_HEADERS_CURL_ARGS uses the --silent option and PAGE_CONTENT_CURL_ARGS does not (though there's no intention behind this omission). However, the #page_content method should also use the --silent flag, to prevent progress bar text (#=#=#, etc.) from appearing in output.

This is an issue because the regex that's used to identify curl error messages in stderr (^curl:.+$/) will fail if leading progress bar text is present. This leads to an ambiguous "cURL failed without a detectable error" message instead of the actual error message(s) from curl.

This PR addresses the issue by adding --silent to Livecheck::Strategy::DEFAULT_CURL_ARGS, which both PAGE_HEADERS_CURL_ARGS and PAGE_CONTENT_CURL_ARGS inherit.

[BrewTestBot]

Review period skipped due to critical label.

[MikeMcQuaid]

Thanks again @samford!