🧪 Make a draft based plugin bump PR CI trigger

Normally, PRs/commits published using the default GitHub Actions CI/CD
API token are not propagated to any integrations. This patch marks the
plugin update PR as a draft and leaves a comment asking the maintainers to
mark it as ready for review in order to actually trigger a CI run.

This idea is found in GitHub's own repos:
* github/codeql-action#2263 (comment)
* https://github.com/github/codeql-action/blob/4ebadbc7/.github/workflows/update-dependencies.yml#L38-L41
* github/codeql-action#1868
* github/codeql-action#679

.github/workflows/test.yml

@@ -14,6 +14,11 @@ on:
     branches:
       - main
       - "[0-9]+.[0-9]+.x"
+    types:
+    - opened  # default
+    - synchronize  # default
+    - reopened  # default
+    - ready_for_review  # used in PRs created from the release workflow
 
 env:
   PYTEST_ADDOPTS: "--color=yes"

.github/workflows/update-plugin-list.yml

@@ -46,6 +46,7 @@ jobs:
         run: python scripts/update-plugin-list.py
 
       - name: Create Pull Request
+        id: pr
         uses: peter-evans/create-pull-request@6d6857d36972b65feb161a90e484f2984215f83e
         with:
           commit-message: '[automated] Update plugin list'
@@ -55,3 +56,13 @@ jobs:
           branch-suffix: short-commit-hash
           title: '[automated] Update plugin list'
           body: '[automated] Update plugin list'
+          draft: true
+
+      - name: Instruct the maintainers to trigger CI by undrafting the PR
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+        run: >-
+          gh pr comment
+          --body 'Please mark the PR as ready for review to trigger PR checks.'
+          --repo '${{ github.repository }}'
+          '${{ steps.pr.outputs.pull-request-number }}'