.github: better downloading of promtool

Signed-off-by: paulfantom <[email protected]>

.github/workflows/prometheusrule.yml

@@ -15,5 +15,10 @@ jobs:
       - uses: actions/setup-go@v2
         with:
           go-version: '1.15'
-      - run: go get -u github.com/prometheus/prometheus/cmd/promtool
-      - run: verify-prometheus-rules.sh
+      - run: go get -u github.com/brancz/gojsontoyaml
+      #- run: go get -u github.com/prometheus/prometheus/cmd/promtool
+      - name: Download latest release of promtool
+        run: |
+          VERSION=$(curl -s https://api.github.com/repos/prometheus/prometheus/releases/latest | grep "tag_name" | awk '{print substr($2, 2, length($2)-3)}' | sed 's/v//')
+          curl -s -L "https://github.com/prometheus/prometheus/releases/download/v${VERSION}/prometheus-${VERSION}.linux-amd64.tar.gz" | tar -zxf - -C "${GITHUB_WORKSPACE}/" --strip-components 1 "prometheus-${VERSION}.linux-amd64/promtool"
+      - run: PATH="${PATH}:${GITHUB_WORKSPACE}" ./hack/verify-prometheus-rules.sh