darwin: Bump MAXOSX_DEPLOYMENT_TARGET to 10.13
This bumps the minumum supported version to 10.13 (High Sierra) which is 6 years old at this point.
Fixes #22938 (closed)
Due to a large amount of spam we do not allow new users to create repositories, they are "external" users. If you are a new user and want to create a repository, for example for forking GHC, open a new issue on ghc/ghc using the "get-verified" issue template
This bumps the minumum supported version to 10.13 (High Sierra) which is 6 years old at this point.
Fixes #22938 (closed)