ensure go version for tests

Signed-off-by: Daniel Holbach <daniel@weave.works>

.github/workflows/on-pr.yaml

@@ -10,6 +10,15 @@ jobs:
     steps:
       - name: checkout
         uses: actions/checkout@v2
+      - name: Find go version
+        run: |
+          GO_VERSION=$(awk '/^go/ {print $2};' go.mod)
+          echo "::set-output name=version::${GO_VERSION}"
+        id: awk_gomod
+      - name: Ensure go version
+        uses: actions/setup-go@v2
+        with:
+          go-version: "${{ steps.awk_gomod.outputs.version }}"
       - name: run tests
         run: go test -json ./... > test.json
       - name: Annotate tests