This reduces the test time by ~33% on my system (23s to 15s)
Given that it takes ~180-240s on Github Actions, if we get a reduction
like that we can save over a minute.
This is run in the current locale, without resetting to en_US.UTF-8
like our integration tests do.
So if you want to check for a specific message you need to check the
localized version.
Make sure to also look for the error part that occurs after the last format
specifier.
Still not great because it won't fail if there's unexpected output at the
beginning or end of the string.
I had originally created a safe `set_locale()` wrapper and clippy-disallowed
`libc::setlocale()` but almost all our uses of `libc::setlocale()` are in a loop
where it makes much more sense to just obtain the lock outright then call
`setlocale()` repeatedly rather than lock it in the wrapper function each time.
