Use v6 of actions/checkout

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: alexdewar

.github/workflows/pre-commit-autoupdate.yml

@@ -13,7 +13,7 @@ jobs:
   auto-update:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v5
       - uses: browniebroke/pre-commit-autoupdate-action@1
       - uses: peter-evans/create-pull-request@v7