github: Revert failed experiment (re: 2e6c56df, 9ad9a1de, 5c389035)

.github/workflows/ci.yml:
- Go back to wrapping the regression tests in script(1).

src/cmd/ksh93/data/builtins.c:
- Never mind about the stty builtin.

src/cmd/ksh93/tests/pty.sh:
- Refuse to run if there isn't a functioning tty.
- Make sure stty(1) works on /dev/tty by redirecting stdin.

.github/workflows/ci.yml

@@ -19,14 +19,14 @@ jobs:
         export TZ=UTC
         ulimit -n 1024
         : default regression tests &&
-        bin/shtests &&
+        script -q -e -c "bin/shtests" &&
         : regression tests with OS-provided UTF-8 locales &&
-        LANG=nl_NL.UTF-8 bin/shtests --locale --nocompile &&
-        LANG=ja_JP.UTF-8 bin/shtests --locale --nocompile &&
+        LANG=nl_NL.UTF-8 script -q -e -c "bin/shtests --locale --nocompile" &&
+        LANG=ja_JP.UTF-8 script -q -e -c "bin/shtests --locale --nocompile" &&
         : disable most SHOPTs, rebuild ksh &&
         sed --regexp-extended --in-place=.orig \
           '/^SHOPT (2DMATCH|AUDIT|BGX|BRACEPAT|DYNAMIC|EDPREDICT|ESH|FIXEDARRAY|HISTEXPAND|MULTIBYTE|NAMESPACE|OPTIMIZE|SUID_EXEC|STATS|VSH)=/ s/=1/=0/' \
           src/cmd/ksh93/SHOPT.sh &&
         bin/package make &&
         : default regression tests with SHOPTs disabled &&
-        bin/shtests
+        script -q -e -c "bin/shtests"