ci: Refactor/fix external contribution handling (#12724)

This should fix the old behavior...

previously, we made a PR against a PR branch when we detected that it
was opened by an external contributor. This is problematic, turns out,
because external contributors will usually have a fork of the repo and
thus the action will fail.

Now, instead, we will make a PR against develop when a contributor PR is
_merged_.

See example PR:
#12728

Author: mydea

.github/workflows/build.yml

@@ -229,44 +229,6 @@ jobs:
           message: |
             ⚠️ This PR is opened against **master**. You probably want to open it against **develop**.
 
-  job_external_contributor:
-    name: External Contributors
-    needs: job_install_deps
-    runs-on: ubuntu-20.04
-    if: |
-      github.event_name == 'pull_request'
-      && (github.event.action == 'opened' || github.event.action == 'reopened')
-      && github.event.pull_request.author_association != 'COLLABORATOR'
-      && github.event.pull_request.author_association != 'MEMBER'
-      && github.event.pull_request.author_association != 'OWNER'
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
-      - name: Set up Node
-        uses: actions/setup-node@v4
-        with:
-          node-version-file: 'package.json'
-      - name: Check dependency cache
-        uses: actions/cache/restore@v4
-        with:
-          path: ${{ env.CACHED_DEPENDENCY_PATHS }}
-          key: ${{ needs.job_install_deps.outputs.dependency_cache_key }}
-          fail-on-cache-miss: true
-
-      - name: Add external contributor to CHANGELOG.md
-        uses: ./dev-packages/external-contributor-gh-action
-        with:
-          name: ${{ github.event.pull_request.user.login }}
-      - name: Create PR with changes
-        uses: peter-evans/create-pull-request@v6
-        with:
-          commit-message: "ref: Add external contributor to CHANGELOG.md"
-          title: "ref: Add external contributor to CHANGELOG.md"
-          branch: 'external-contributor/patch-${{ github.event.pull_request.user.login }}'
-          delete-branch: true
-          body: This PR adds the external contributor to the CHANGELOG.md file, so that they are credited for their contribution.
-
   job_build:
     name: Build
     needs: [job_get_metadata, job_install_deps]

.github/workflows/external-contributors.yml

@@ -0,0 +1,44 @@
+name: "CI: Mention external contributors"
+on:
+  pull_request:
+    types:
+      - closed
+    branches:
+      - develop
+
+jobs:
+  external_contributor:
+    name: External Contributors
+    runs-on: ubuntu-20.04
+    if: |
+      github.event.pull_request.author_association != 'COLLABORATOR'
+      && github.event.pull_request.author_association != 'MEMBER'
+      && github.event.pull_request.author_association != 'OWNER'
+      && github.actor != 'dependabot[bot]'
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: 'package.json'
+          cache: 'yarn'
+
+      - name: Install dependencies
+        run: yarn install --frozen-lockfile
+
+      - name: Add external contributor to CHANGELOG.md
+        uses: ./dev-packages/external-contributor-gh-action
+        with:
+          name: ${{ github.event.pull_request.user.login }}
+      - name: Create PR with changes
+        uses: peter-evans/create-pull-request@c5a7806660adbe173f04e3e038b0ccdcd758773c
+        with:
+          commit-message: "ref: Add external contributor to CHANGELOG.md"
+          title: "ref: Add external contributor to CHANGELOG.md"
+          branch: 'external-contributor/patch-${{ github.event.pull_request.user.login }}'
+          base: 'develop'
+          delete-branch: true
+          body: This PR adds the external contributor to the CHANGELOG.md file, so that they are credited for their contribution.
+