Dongsu Park 730ae31678 .github: skip branch checkout if it exists
In case the target branch already exists, `checkout_branch()` needs to
simply `exit 0`, so the subsequent steps could be skipped.
In that case, it has to set `UPDATE_NEEDED` to 0, so the Github action
could avoiding creating another PR.

It resolves occasional issues that happen when subsequent PRs overwrite
existing open PRs made on the very same version. It would be no problem
if there was no change in the PR. However, if there was any manual
change in the previous open PR, the change will be simply overwritten.
That would be very unfortunate.
2020-07-23 18:32:27 +02:00
..