chore(ci): remove dependabot auto-merge workflow (#4964)

Dependabot minor/patch updates were auto-approved by github-actions[bot],
which satisfied master's required review and merged straight to master.
All dependency updates go back to manual review. The workflow has also
been removed from dgibbs64/repo-sync so it is not synced back.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/action-dependabot-automerge.yml

@@ -1,27 +0,0 @@
-name: Dependabot auto-merge
-
-on: pull_request
-
-permissions:
-  contents: write
-  pull-requests: write
-
-jobs:
-  dependabot:
-    runs-on: ubuntu-latest
-    if: github.actor == 'dependabot[bot]'
-    steps:
-      - name: Fetch dependabot metadata
-        id: metadata
-        uses: dependabot/fetch-metadata@v2
-        with:
-          github-token: "${{ secrets.GITHUB_TOKEN }}"
-
-      - name: Approve and enable auto-merge for minor/patch updates
-        if: steps.metadata.outputs.update-type != 'version-update:semver-major'
-        env:
-          PR_URL: ${{ github.event.pull_request.html_url }}
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: |
-          gh pr review --approve "$PR_URL"
-          gh pr merge --auto --squash "$PR_URL"