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.

.github/workflows/ci.yml

@@ -14,13 +14,19 @@ jobs:
       run: bin/package make
     - name: Regression tests
       run: |
+        PS4="$PS4 [ci.yml] "
+        set -o xtrace
         export TZ=UTC
         ulimit -n 1024
+        : default regression tests &&
         script -q -e -c "bin/shtests" &&
+        : regression tests with OS-provided UTF-8 locales &&
         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|HISTEXPAND|MULTIBYTE|NAMESPACE|OPTIMIZE|SUID_EXEC|STATS|VSH)=/ s/=1/=0/' \
+          '/^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 &&
         script -q -e -c "bin/shtests"