Update script to push new commits after tagging

[absoludity]

Currently the script creates a new release on the current branch, tagging the local commit then pushing the tag, but not pushing the commits to the upstream branch.

We could instead:

1. Ensure the branch is up-to-date at the beginning
2. commit new package dir to the branch (as now)
3. tag and push both the tag and the branch

If pushing the commits is last, if it fails it can be resolved without disturbing the release.