Update generate-changelog.yml

The github action for generating the changelog is failing. advice from smokyboo is to bump the action to v4 which should give us the correct version

.github/workflows/generate-changelog.yml

@@ -7,7 +7,7 @@ jobs:
   changelog:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Generate Changelog
         run: |
           gem install github_changelog_generator