Update actions/checkout action to v7 (#261)

Co-authored-by: oxide-renovate[bot] <146848827+oxide-renovate[bot]@users.noreply.github.com>

Author: oxide-renovate[bot]

.github/workflows/rust.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7
 
       - name: generate documentation
         run: cargo doc --no-deps