Workflow fixes

- Use a current, maintained version of `actions/setup-python`
- Use branch pattern matching so we don't have to update the action for each new version branch (see https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#filter-pattern-cheat-sheet)

Author: tokebe

.github/workflows/pr-checks.yml

@@ -3,7 +3,7 @@ name: PR checks
 on:
   pull_request:
   push:
-    branches: [master, main, 2.0]
+    branches: [master, main, 'v?[0-9]+.[0-9]+**']
 jobs:
   linting:
     name: Check Yamllint
@@ -15,7 +15,7 @@ jobs:
           ref: ${{ github.event.pull_request.head.ref }}
           repository: ${{ github.event.pull_request.head.repo.full_name }}
       - name: Set up Python 3.13
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v6
         with:
           python-version: '3.13'
       - name: Install deps
@@ -36,7 +36,7 @@ jobs:
           ref: ${{ github.event.pull_request.head.ref }}
           repository: ${{ github.event.pull_request.head.repo.full_name }}
       - name: Set up Python 3.13
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v6
         with:
           python-version: '3.13'
       - name: Install deps