tests: Stop ignoring test failures on macOS

Test failures were previously ignored on macOS because there are 12 tests which consistently fail (and have not yet been fixed, because there are no regularly active macOS maintainers for GLib; you could help here!).

However, this means that new test failures can’t be spotted.

So, explicitly mark those 12 tests as should_fail on macOS, and then make other test failures cause failure of the CI run.

We can track the process of fixing those 12 tests on #1392 and #1251.

Signed-off-by: Philip Withnall pwithnall@endlessos.org

Helps: #1392