ci: add release-commenter (#710)

Author: fgreinacher

.github/workflows/ci.yml

@@ -112,3 +112,11 @@ jobs:
         with:
           tag_name: v${{ steps.nbgv.outputs.SemVer2 }}
           release_name: v${{ steps.nbgv.outputs.SemVer2 }}
+      - name: Comment relevant issues and merge requests
+        uses: apexskier/github-release-commenter@v1.2
+        with:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          comment-template: |
+            This is addressed in release {release_link}.
+          label-template: |
+            state: released