Fix disabling SHOPT_FIXEDARRAY (re: 2182ecfa)

It was easier than expected to fix this one. The many regression
test failures caused by disabling it were all due to one bug:
'typeset -p' output broke when building without this option.

src/cmd/ksh93/sh/nvtree.c: nv_attribute():
- In this function to print the attributes of a name-value pair,
  move four lines of code out of #if SHOPT_FIXEDARRAY...#endif that
  were inadvertently moved into the #if block in ksh93 2012-05-18.
  See the changes to nvtree.c in this multishell repo commit:
  aabab56a

src/cmd/ksh93/data/builtins.c:
- Update/rewrite 'typeset -a' documentation.
- Make it adapt to SHOPT_FIXEDARRAY.
- Fix a few typos.

src/cmd/ksh93/tests/arrays2.sh:
- Only one regression test needs a SHOPT_FIXEDARRAY check.

.github/workflows/ci.yml:
- Disable SHOPT_FIXEDARRAY when regression-testing without SHOPTs.
- Enable xtrace, add ':' commands for traced comments. This should
  make the CI runner output logs a little more readable.

src/cmd/ksh93/sh/nvtree.c

@@ -524,11 +524,11 @@ void nv_attribute(register Namval_t *np,Sfio_t *out,char *prefix,int noname)
 				break;
 			}
 		}
-#if SHOPT_FIXEDARRAY
 		if(fp)
 			outtype(np,fp,out,prefix);
 		if(noname)
 			return;
+#if SHOPT_FIXEDARRAY
 		if(fixed)
 		{
 			sfprintf(out,"%s",nv_name(np));