Add source-keyed target cache

.github/workflows/target-key.yml

@@ -0,0 +1,29 @@
+name: target-key
+
+on: [push, pull_request]
+
+permissions: {}
+
+jobs:
+  target-key:
+    if: github.repository == 'Swatinem/rust-cache'
+    runs-on: ubuntu-latest
+
+    env:
+      CARGO_TERM_COLOR: always
+
+    steps:
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+        with:
+          persist-credentials: false
+
+      - run: rustup toolchain install stable --profile minimal --no-self-update
+
+      - uses: ./
+        with:
+          workspaces: tests
+          cache-workspace-crates: "true"
+          target-key: ${{ hashFiles('tests/**/*.rs', 'tests/Cargo.toml', 'tests/Cargo.lock') }}
+
+      - run: cargo build --release
+        working-directory: tests