GitHub Actions now supports a concurrency key at both the workflow and job level that will ensure that only a single run or job is in progress.
There are a number of scenarios where you only want a single instance of a particular workflow or job running at any given time. For example: if you have a deployment to your production environment ensuring that only a single deployment is happening at any given time and that you are always deploying the latest code can be important. The concurrency key can be any string or an expression using the github context. When a job or run starts it first checks to see if anything is currently holding on to the concurrency group specified. If not, it will start. If there is a lock on the group, the job or run will be marked as pending and will only start after the blocking job or run completes.
Learn more about concurrency groups in GitHub Actions