fix: pin GitHub Actions to SHA for supply chain security (#10)

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

Author: riccardosarro

.github/workflows/rust.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@50fbc622fc4ef5163becd7fab6573eac35f8462e # v1
     - name: Build
       run: cargo build --verbose
     - name: Run tests