github actions: try caching the module cache

.github/workflows/go.yml

@@ -23,6 +23,14 @@ jobs:
     - name: Check out code into the Go module directory
       uses: actions/checkout@v2
 
+    - name: Share cache with other actions
+      uses: actions/cache@v2
+      with:
+        path: ~/go/pkg/mod
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-go-
+
     - name: Ensure all files were formatted as per gofmt
       run: |
         gofmt -l $(find . -name '*.go') >/dev/null
@@ -50,6 +58,14 @@ jobs:
     - name: Check out code into the Go module directory
       uses: actions/checkout@v2
 
+    - name: Share cache with other actions
+      uses: actions/cache@v2
+      with:
+        path: ~/go/pkg/mod
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-go-
+
     - name: Test
       run: |
         go test -v -race ./internal/...
@@ -69,6 +85,14 @@ jobs:
     - name: Check out code into the Go module directory
       uses: actions/checkout@v2
 
+    - name: Share cache with other actions
+      uses: actions/cache@v2
+      with:
+        path: ~/go/pkg/mod
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-go-
+
     - name: Build Docker container with the tools our tests require
       run: |
         docker build --pull --no-cache --rm -t=router7 -f travis/Dockerfile .