Currently our release process is kicked off whenever a PR is merged and there are no changesets within the `.changeset` directory. Typically this happens when we intend to publish a release, just after we merge a "Version Packages" PR which removes the changesets and adds the entries to our changelog.
However, this also means that merging any PR without user-facing changes during the period after we've made a release will trigger another release (which luckily fails because the created tag already exists on the remote. See #184).
This change avoids that scenario by fetching tags when checking out the repo. Now when `npx changeset tag` runs, it will see that the tag already exists and skip creating it (`🦋 Skipping tag (already exists): v3.3.2`). The `git push --tags` step will no longer throw an error ("Everything up-to-date"). And lastly, the publish step won't get triggered because the output from `npx changeset tag` doesn't contain the string `"New tag:"`. The action should just finish successfully with nothing to left do.
Fixes#184
