Use cargo-llvm-cov baked into the rust-ci image instead of caching

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.forgejo/workflows/ci.yml

@@ -101,21 +101,8 @@ jobs:
           restore-keys: |
             sccache-${{ runner.os }}-
 
-      # Not baked into the rust-ci image (see docker/rust-ci in
-      # infrastructure) — cache the compiled binary rather than bumping
-      # the shared image just for this one project. To upgrade, change the
-      # version here, in the cache key, and in the install command below.
-      - name: Cache cargo-llvm-cov binary
-        uses: actions/cache@v4
-        with:
-          path: ~/.cargo/bin/cargo-llvm-cov
-          key: cargo-llvm-cov-${{ runner.os }}-0.9.1
-
-      - name: Install cargo-llvm-cov
-        run: |
-          rustup component add llvm-tools-preview
-          command -v cargo-llvm-cov >/dev/null 2>&1 || cargo install cargo-llvm-cov --locked --version 0.9.1
-
+      # cargo-llvm-cov and llvm-tools-preview are baked into the rust-ci
+      # image (see docker/rust-ci in infrastructure).
       # Reports coverage only — no --fail-under-lines yet. main.rs is
       # excluded: thin argv dispatch exercised by the real end-to-end
       # `cargo run`, not unit tests, so it's not a meaningful signal here.