ci: Enable actions/cache for Go modules

.github/workflows/test.yaml

@@ -26,6 +26,12 @@ jobs:
       with:
         go-version: '^1.17.7'
     - run: go version
+    - uses: actions/cache@v2
+      with:
+        path: ~/go/pkg/mod
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-go-
     - name: Install kubebuilder
       run: |
         curl -L -O https://github.com/kubernetes-sigs/kubebuilder/releases/download/v2.3.2/kubebuilder_2.3.2_linux_amd64.tar.gz