ci: add action cache to reduce workflow time

Signed-off-by: Changyuan Lyu <changyuanl@google.com>

.github/workflows/rust.yml

@@ -20,6 +20,15 @@ jobs:
 
     steps:
       - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
+      - uses: actions/cache@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9 # v4.0.2
+        with:
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            target/
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
       - name: Build
         run: cargo build --verbose
       - name: Format