chore(ci): Update actions/checkout action to v6 (#71)

Author: renovate[bot]

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
           - py311
           - py310
     steps:
-        - uses: actions/checkout@v5
+        - uses: actions/checkout@v6
         - uses: prefix-dev/[email protected]
           with:
             pixi-version: "latest"
@@ -31,7 +31,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Setup Pixi
         uses: prefix-dev/[email protected]
       - name: Format and lint