Add log message when worker lock timeouts get large

[devonh]

This is to help track down a possible, but very rare, worker deadlock that was seen on matrix.org.
In theory, you could work back from an instance of these new logs to the approximate time when the lock was obtained and focus the diagnostic efforts there.

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
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  (run the linters)