Fix and enhance print-gittxt.sh

• Fix print-gittxt.sh with git-worktree
• Tweak git invocations in print-gittxt.sh
  1. Use the --abbrev-ref argument to git-rev-parse instead of sed.
  2. Discard output from the check for origin/master, -q is "only meaningful in --verify mode".
  3. Pass --no-pager to get plain output when testing interactively.
• Exclude all ancestors of the merge base in print-gittxt.sh
• Use data from CI in print-gittxt.sh

Closes #6061 (closed)