.github/workflows/autobranch.yml: Add "master" autobranch
Now that we have transitioned from "master" to "main" branch, add a "master" autobranch that will track "main" with extra warnings in the doc, the code and the shell scripts.
Now that we have transitioned from "master" to "main" branch, add a "master" autobranch that will track "main" with extra warnings in the doc, the code and the shell scripts.