Reduce number of tasks that run on macos

Currently we run a full matrix build on all OS's, which includes every server version, every cluster configuration, etc.

I think we can get away with a lot less for macos, since it's essentially the same as Linux in most regards.

We should run against replica set, with auth + ssl, against 5.0 and latest servers only. And also any compression tests, to make sure we test native libraries.