Run clippy with --frozen, ensuring that Cargo.lock is up to date

.github/workflows/rust-tests.yml

@@ -31,10 +31,13 @@ jobs:
       - name: Check formatting
         run: cargo fmt -- --check
 
+      - name: Fetch dependencies
+        run: cargo fetch --locked
+
       - uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
-          args: --all-features --all-targets -p nethsm_pkcs11  -- -D warnings --no-deps
+          args: --all-features --frozen --all-targets -p nethsm_pkcs11  -- -D warnings --no-deps
 
   check-windows:
     runs-on: windows-latest