ci: speed up build-ksud again (#54)

.github/workflows/build-ksud.yml

@@ -29,9 +29,15 @@ jobs:
           ~/.cargo/registry/index/
           ~/.cargo/registry/cache/
           ~/.cargo/git/db/
-          target/            
         key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
         restore-keys: ${{ runner.os }}-cargo-
+    - name: Set up ksud build cache
+      uses: actions/cache@v3
+      continue-on-error: false
+      with:
+        path: ./userspace/ksud/target/
+        key: ${{ runner.os }}-ksud-${{ hashFiles('**/Cargo.lock') }}-${{ matrix.target }}
+        restore-keys: ${{ runner.os }}-ksud-
     - name: Build ksud
       uses: actions-rs/cargo@v1
       with: