github actions: Align cmake step names with the autotools build.

Make it a little more clear how steps correspond, and add 'build'
to both workflow names so the intention of the runs is explicit
on the actions page.
2 jobs for master in 49 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed autoconf #11907
docker

00:00:49

passed cmake #11908
docker

00:00:18