More misc. tweaks and cleanups

Notable changes:

.github/workflows/ci.yml:
- Run 'bin/package test' on the github runner so we test iffe too.

src/cmd/ksh93/sh/subshell.c:
- sh_assignok was usually called like 'np = sh_assignok(np,0)'. But
  the function never changes np, it just returns the np value
  passed to it, so the assignment is pointless and that function
  can be changed to a void.

src/cmd/ksh93/sh/fault.c: sh_fault():
- Remove check for sh.subshell after sh_isstate(SH_INTERACTIVE). As
  of 48ba6964, it is never set in subshells.

src/cmd/ksh93/tests/variables.sh

@@ -36,7 +36,7 @@ fi
 # use the same pseudorandom seed as the main shell.
 # https://github.com/ksh93/ksh/issues/285
 # These tests sometimes fail as duplicate numbers can occur randomly, so try up to $N times.
-integer N=3 i rand1 rand2
+integer N=5 i rand1 rand2
 RANDOM=123
 function rand_print {
 	ulimit -t unlimited 2> /dev/null
@@ -81,7 +81,7 @@ do	( echo $RANDOM & ) >|r1
 	do	((giveup)) && break
 	done
 	if	((giveup))
-	then	err_exit "Test 4: ( echo $RANDOM & ) does not write output"
+	then	err_exit 'Test 4: ( echo $RANDOM & ) does not write output'
 	fi
 	kill $! 2>/dev/null
 	trap - USR1