⬆️ Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
   format:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Prepare stylua
         run: |
           curl -Lo /tmp/stylua-linux.zip https://github.com/JohnnyMorganz/StyLua/releases/download/v${STYLUA_VERSION}/stylua-linux.zip