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

The org ruleset now requires 1 approving review + code-owner review, so
auto-merge can never complete without a human approval — the workflow
only added a no-op (or erroring) check to every PR. Repo-level 'Allow
auto-merge' was also disabled on several repos, making the gh pr merge
--auto call fail benignly. The required-workflow rule referencing this
file was removed from org ruleset 15869156 first.

.github/workflows/dependabot-auto-merge.yaml

@@ -1,27 +0,0 @@
-name: Dependabot Auto-Merge
-
-on:
-  pull_request:
-    types: [opened, synchronize]
-  workflow_call: {}
-
-permissions:
-  contents: write
-  pull-requests: write
-
-jobs:
-  auto-merge:
-    runs-on: ubuntu-latest
-    timeout-minutes: 5
-    steps:
-      - name: Fetch Dependabot metadata
-        if: github.actor == 'dependabot[bot]'
-        uses: dependabot/fetch-metadata@v2
-        id: metadata
-
-      - name: Enable auto-merge for non-major updates
-        if: github.actor == 'dependabot[bot]' && steps.metadata.outputs.update-type != 'version-update:semver-major'
-        run: gh pr merge --auto --squash "$PR_URL"
-        env:
-          PR_URL: ${{ github.event.pull_request.html_url }}
-          GH_TOKEN: ${{ github.token }}