cache go modules

.github/workflows/test.yml

@@ -21,5 +21,12 @@ jobs:
     - name: Install Go
       uses: actions/setup-go@v2
 
+    - uses: actions/cache@v2
+      with:
+        path: ~/go/pkg/mod
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-go-
+
     - name: Build
       run: make all