Update the build badge from Concourse to GitHub Actions (#1027)

Author: ialidzhikov

README.md

@@ -1,7 +1,7 @@
 # machine-controller-manager
 
 [![REUSE status](https://api.reuse.software/badge/github.com/gardener/machine-controller-manager)](https://api.reuse.software/info/github.com/gardener/machine-controller-manager)
-[![CI Build status](https://concourse.ci.gardener.cloud/api/v1/teams/gardener/pipelines/machine-controller-manager-master/jobs/master-head-update-job/badge)](https://concourse.ci.gardener.cloud/teams/gardener/pipelines/machine-controller-manager-master/jobs/master-head-update-job)
+[![Build](https://github.com/gardener/machine-controller-manager/actions/workflows/non-release.yaml/badge.svg)](https://github.com/gardener/machine-controller-manager/actions/workflows/non-release.yaml)
 [![Go Report Card](https://goreportcard.com/badge/github.com/gardener/machine-controller-manager)](https://goreportcard.com/report/github.com/gardener/machine-controller-manager)
 
 **Note**