Always push the branch in the Merge command

[sbesson]

The current design was implemented for repositories with lots of open requests in mind so that the merge branch is always updated. However, for repositories or development branches with few PRs opened, the requirement can mean the merge branch never gets updated to the HEAD of the development branch if all PRs are closed or excluded.

This commit removes this restriction by pushing unconditionally the merge branch when the --push argument is passed.

/cc @joshmoore

[joshmoore]

Change makes sense unless something breaks and we realize we need a --force-push (or similar)

[sbesson]

--force-push is an option but would require to modify semantics across the CI board which looks like unnecessary work. I am more inclined to call this a bug and have the --push option semantically meaning force pushing.

[joshmoore]

Fair enough.