Update automerge configuration to use Squash and Merge (#72)

since this repo now only allows squash-and-merge, the automerging
funcitonality for dependabot PRs needs to be updated to squash and merge
- see also https://cli.github.com/manual/gh_pr_merge

.github/workflows/auto_merge.yml

@@ -23,7 +23,7 @@ jobs:
           GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
       - name: Enable auto-merge for Dependabot PRs
         if: ${{ steps.metadata.outputs.update-type == 'version-update:semver-patch' || steps.metadata.outputs.update-type == 'version-update:semver-minor'}}
-        run: gh pr merge --auto --merge "$PR_URL"
+        run: gh pr merge --auto --squash "$PR_URL"
         env:
           PR_URL: ${{github.event.pull_request.html_url}}
           GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}