ProtectedBranches: log pushed_refs in debug mode

[jawshooah]

This will help in debugging #271.

[sds]

Printing debug messages breaks the output of the hook with the way we currently output OK/FAIL at the end of the hook's run, so I'd be hesitant to commit this in even if it only appeared with OVERCOMMIT_DEBUG=1.

This has come up a few times, so it seems like we need to expose a call that allows a hook to aggregate log messages which are printed in addition to its regular output when debugging is enabled (but printed at the end of the hook run).

[jawshooah]

Makes sense. We'd need to gate the run in a begin...ensure block so that log messages are printed even if the hook run throws an exception.

[sds]

Going to close this since the original issue seems quiet, and I'd rather not commit something to master to help what appears to be a user hitting an edge case of some sort, given @jawshooah's difficulty in reproducing the issue.