CI: temporarily remove coverage from macOS job

Currently the macOS job is failing because IO is not building,
which is requiring by the code coverage system, and this causes the
job to fail. See:

gap-system#4374

By adding NO_COVERAGE=1 to this job, IO will no longer need
to be compiled. Obviously, in the long term we want coverage on this
job, and we want to be able to compile IO, but this will get the
CI running for the rest of GAP in a non-controversial way in the
meantime, I hope.

.github/workflows/CI.yml

@@ -86,7 +86,7 @@ jobs:
 
  - os: macos-latest
  test-suites: "docomp testinstall"
- extra: "BOOTSTRAP_MINIMAL=yes"
+ extra: "BOOTSTRAP_MINIMAL=yes NO_COVERAGE=1"
 
  # test creating the manual
  # TODO: make the resulting HTML and PDF files available as build