[PM-29567] Cache cargo-run-bin tools in the lint workflow

cargo-run-bin builds its tools into .bin, which was not cached, so every lint
check rebuilt its tools from source each run.

Cache .bin with a dedicated actions/cache step rather than via rust-cache's
cache-directories. rust-cache keys every matrix check under one shared
job-based key (so only the first check to save wins, and the others rebuild
their tools anyway) and folds in the Cargo.lock hash (which rotates every day
or two). The tools depend only on their pinned versions and the toolchain, so
key on Cargo.toml + rust-toolchain.toml per check instead, with restore-keys
for graceful fallback.

Author: coroiu

.github/workflows/lint.yml

@@ -97,6 +97,20 @@ jobs:
         if: matrix.needs_rust
         uses: Swatinem/rust-cache@779680da715d629ac1d338a641029a2f4372abb5 # v2.8.2
 
+      # Cache cargo-run-bin's built tools (.bin) separately from rust-cache. The
+      # tools depend only on their pinned versions (Cargo.toml) and the toolchain,
+      # not on Cargo.lock, so this key avoids rust-cache's lockfile rotation. Keyed
+      # per check so each one caches only the tools it builds, with no contention
+      # (rust-cache keys all matrix checks under one shared job-based key).
+      - name: Cache cargo-run-bin tools
+        if: matrix.needs_rust
+        uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
+        with:
+          path: .bin
+          key: cargo-bin-${{ runner.os }}-${{ matrix.check }}-${{ hashFiles('Cargo.toml', 'rust-toolchain.toml') }}
+          restore-keys: |
+            cargo-bin-${{ runner.os }}-${{ matrix.check }}-
+
       - name: Install cargo-run-bin
         if: matrix.needs_rust
         run: cargo install cargo-run-bin --locked --version 1.7.4