Automatically update changelog in the repo after release

.github/workflows/update-changelog.yaml

@@ -0,0 +1,33 @@
+# This workflow takes the GitHub release notes an updates the changelog on the
+# master branch with the body of the release notes, thereby keeping a log in
+# the git repo of the changes.
+
+name: "Update Changelog"
+
+on:
+  workflow_dispatch:
+  release:
+    types: [released]
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+        with:
+          ref: master
+
+      - name: Update Changelog
+        uses: stefanzweifel/changelog-updater-action@v1
+        with:
+          release-notes: ${{ github.event.release.body }}
+          latest-version: ${{ github.event.release.name }}
+
+      - name: Commit updated CHANGELOG
+        uses: stefanzweifel/git-auto-commit-action@v4
+        with:
+          branch: master
+          commit_message: Update CHANGELOG
+          file_pattern: CHANGES.md

RELEASING.md

@@ -2,11 +2,10 @@
 
 To make a new release of pytest-mpl follow the following steps:
 
-* Update the chanelog with the date of the release, and ensure that all relevant PRs have changelog entries.
-* Push the chanelog to master (via a PR)
-* Ensure the sdist and wheel GitHub Actions jobs succeeded on master after the merge of the changelog.
+* Ensure the sdist and wheel GitHub Actions jobs succeeded on master after the last merge.
 * Also ensure that the tarball built has an autogenerated version number from setuptools_scm.
-* Tag the new release, using the format `vX.Y.X`.
-* Push the tag with `git push upstream master --follow-tags`
-* Watch as GitHub actions builds the sdist and universal wheel and pushes them to PyPI for you.
+* Write the release notes in the GitHub releases UI, use the autogenerated
+  notes and tidy up a little.
+* Publish the new release, using the format `vX.Y.X`.
+* Watch as GitHub actions builds the sdist and universal wheel and pushes them to PyPI for you, and updates CHANGES.md on the master branch.
 * Enjoy the beverage of your choosing 🍻.