Update Ubuntu and checkout versions in changelog check

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

.github/workflows/changelog.yml

@@ -7,10 +7,10 @@ on:
 jobs:
   check-changelog-entry:
     name: changelog entry
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           # `towncrier check` runs `git diff --name-only origin/main...`, which
           # needs a non-shallow clone.