Update actions/checkout action to v7

Author: renovate[bot]

.github/workflows/rust.yml

@@ -12,7 +12,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - name: Build
         run: cargo build --verbose
       - name: Check formatting