.github/workflows/ci.yml:
- Disable Mac build as the GitHub runners appear to be broken
(e.g. SIGCHLD fails, unlike on real Macs) and tend to hang.
- For the Linux build:
- Set GMT timezone for 'printf %T' tests in builtins.sh.
- Set the ulimit for open files to 1024 as the subshell.sh tests
need a lot of open files.
- As the runners lack the POSIX standard /dev/tty device, use the
script command to provide a fake /dev/tty for the bracket.sh
tests that use 'test -t $fd'.
Ref.: https://github.com/actions/runner/issues/241