ci: Greenlight MELPA releases after successfully publishing binaries

Author: ubolonton

.github/workflows/release.yml

@@ -152,3 +152,29 @@ jobs:
       - run: bin/setup
 
       - run: bin/test integ
+
+  publish-melpa:
+    needs: integ
+    runs-on: ubuntu-18.04
+    steps:
+      - name: Set release version
+        run: |
+          echo "RELEASE_VERSION=$(git describe --tags --abbrev=0)" >> $GITHUB_ENV
+
+      - name: Greenlight releasing to MELPA
+        run: |
+          git push origin ${{ env.RELEASE_VERSION }}:refs/heads/release
+        continue-on-error: true
+
+      # We don't want this to trigger workflows, so we don't use a personal access token.
+      - name: Greenlight releasing to MELPA Stable
+        uses: actions/github-script@v4
+        with:
+          script: |
+            github.git.createRef({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              ref: "refs/tags/melpa-stable/v${{ env.RELEASE_VERSION }}",
+              sha: context.sha
+            })
+        continue-on-error: true