shtests: Stop requiring a tty

It is desirable to be able to run the tests on a system without
a functioning tty. Since this distribution comes with its own
pseudo-tty facility, pty, it should be possible to run the few
tests that require a tty on the pseudo-tty instead. I've verified
that they fail as expected on older ksh93.

Discussion: https://github.com/ksh93/ksh/pull/171

src/cmd/ksh93/tests/basic.sh,
src/cmd/ksh93/tests/bracket.sh:
- Remove tests that require a tty.

src/cmd/ksh93/tests/pty.sh:
- Put them here, adapted to work as interactive pty scripts.

src/cmd/ksh93/tests/shtests:
- No longer refuse to run if there is no functioning tty.

.github/workflows/ci.yml:
- Since the tests no longer require a tty, no longer use script(1)
  to get a pseudo-tty. Let's see if this works...
- Re-enable the Mac runner (re: 14632361). Maybe it has improved.

src/cmd/ksh93/tests/shtests

@@ -168,12 +168,6 @@ function valxml
 	return $errors
 }
 
-if	! test -t 1 2>/dev/null 1>/dev/tty
-then	print "The regression tests require a functioning /dev/tty." >&2
-	print "If not available, try script(1) to simulate a tty." >&2
-	exit 128
-fi
-
 command set +o posix 2>/dev/null
 unset DISPLAY FIGNORE HISTFILE POSIXLY_CORRECT _AST_FEATURES
 export ENV=/./dev/null