ci: use actions/checkout@v6

https://github.com/actions/checkout?tab=readme-ov-file#checkout-v6

Author: AviVahl

.github/workflows/tests.yml

@@ -10,7 +10,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, windows-latest, macOS-latest]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version-file: .nvmrc