Treat Manual Backports the same as Meeseeks Backports

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Problem

Manual backports show the manual backport PR instead of the original, because we are looking for the the meeseeks username to resolve backports.

Proposed Solution

The title of the PR should be "Backport PR #{prnumber} on branch {target_branch} ({prtitle})" in either case, so we should look at the PR title using a regex match.

[blink1073]

Fixed in #303