Fix url to kubebuilder binary in workflow

Author: Zach Swanson

.github/workflows/main.yml

@@ -33,7 +33,8 @@ jobs:
         run: |
           os=$(go env GOOS)
           arch=$(go env GOARCH)
-          curl -L https://go.kubebuilder.io/dl/2.3.1/${os}/${arch} | tar -xz -C /tmp/
+          version=2.3.1
+          curl -L https://github.com/kubernetes-sigs/kubebuilder/releases/download/v${version}/kubebuilder_${version}_${os}_${arch}.tar.gz
           sudo mv /tmp/kubebuilder_2.3.1_${os}_${arch} /usr/local/kubebuilder
       - run: make test