[PATCH v6 0/3] refactor t1517 to focus on help output outside a repository

This series refactors t1517-outside-repo.sh to focus on testing `git subcmd -h` outside a Git repository. It does two things:

  1. Moves the existing `update-server-info -h` test to t5200, since it
     tests behavior inside a repo and belongs with other update-server-info
     tests.

  2. Moves the existing `prune -h` test to t5304, since it
     tests behavior inside a repo and belongs with other prune tests.

  3. Introduces a loop in t1517 that automatically verifies `-h` output
     for all main Git subcommands when run outside a repository, using
     the `nongit` helper and `git --list-cmds=main`.

This makes t1517 easier to maintain and ensures that new commands are automatically covered for this class of behavior.

Changes since v5:
- fix instaweb test using PERL prereqs (helped by Ben)

Note: This new iteration is based on 7cd03a555a (builtin/prune: stop depending on 'the_repository', 2025-07-04) commit.

Usman Akinyemi (3):
  t/t1517: automate `git subcmd -h` tests outside a repository
  t5200: move `update-server-info -h` test from t1517
  t5304: move `prune -h` test from t1517

 t/t1517-outside-repo.sh       | 40 +++++++++++++++++++++++------------
 t/t5200-update-server-info.sh |  5 +++++
 t/t5304-prune.sh              |  5 +++++
 3 files changed, 37 insertions(+), 13 deletions(-)