ci: cache rustdoc

Author: crepererum

.github/workflows/ci.yml

@@ -38,9 +38,20 @@ jobs:
           toolchain: stable
           targets: wasm32-wasip2
 
-      - name: Cache
+      - name: Rust Cache
         uses: Swatinem/rust-cache@f13886b937689c021905a6b90929199931d60db1  # v2.8.1
 
+      # Swatinem/rust-cache does NOT cache docs, see
+      # https://github.com/Swatinem/rust-cache/issues/208
+      - name: Rustdoc Cache
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830  # v4
+        with:
+          path: target/doc
+          key: v0-${{ runner.os }}-rustdoc-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            v0-${{ runner.os }}-rustdoc-${{ hashFiles('**/Cargo.lock') }}
+            v0-${{ runner.os }}-rustdoc-
+
       - name: just check
         run: just check
         env: