Upgrade actions/checkout to v6

Author: theypsilon

.github/workflows/rust.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v6
     - name: Build
       run: cargo build --verbose
     - name: Run tests