Expand Livecheck#preprocess_url tests

[samford]

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The existing test for Livecheck#preprocess_url didn't exercise all the existing functionality of this method. This PR expands the test cases to cover the current usage of this method. However, the test cases will need to be expanded again with respect to #9074, as it adds support for additional URL types. We can handle it here, in #9074, or in a follow-up PR, whichever makes the most sense.

The main impetus behind this PR was that #9074 refactors the #preprocess_url method and it originally didn't replicate all of the existing functionality but the issues weren't surfaced by CI. I identified the issues myself but this test should have made this readily apparent. The updated test here clearly points out these issues when run on that PR's original code, so I think it's a good improvement.

[MikeMcQuaid]

Thanks @samford!