Fix slicing of GroupData created from arrays - #20514

Thank you for your contribution to Astropy! 🌌 This checklist is meant to remind the package maintainers who will review this pull request of some common things to look for.

• Do the proposed changes actually accomplish desired goals?
• Do the proposed changes follow the Astropy coding guidelines?
• Are tests added/updated as required? If so, do they follow the Astropy testing guidelines?
• Are docs added/updated as required? If so, do they follow the Astropy documentation guidelines?
• Is rebase and/or squash necessary? If so, please provide the author with appropriate instructions. Also see instructions for rebase and squash.
• Did the CI pass? If no, are the failures related? If you need to run daily and weekly cron jobs as part of the PR, please apply the "Extra CI" label. Codestyle issues can be fixed by the bot.
• Is a change log needed? If yes, did the change log check pass? If no, add the "no-changelog-entry-needed" label. If this is a manual backport, use the "skip-changelog-checks" label unless special changelog handling is necessary.
• Is this a big PR that makes a "What's new?" entry worthwhile and if so, is (1) a "what's new" entry included in this PR and (2) the "whatsnew-needed" label applied?
• At the time of adding the milestone, if the milestone set requires a backport to release branch(es), apply the appropriate "backport-X.Y.x" label(s) before merge.

The test failures aren't from this change. Every failing job stops on the config tests importing astropy.extern.configobj, which was broken at the old base c55a2b2 and is fixed on main. I rebased onto main. Could a maintainer approve the new run?

@astrofrog , what do you think? Exclude from contributor list?

@astrofrog , what do you think? Exclude from contributor list?

	Last 24 hours	Last 7 days
Pull requests opened	5	51
Issues opened	0	33

Hey @pllim , just wanted to jump in and clarify nothing here is automated or running on a bot loop. I’m a real person manually selecting issues, directing the agent's focus, running/verifying the reproductions, and reviewing every diff before opening a PR. Im real haha, I've just been working alot in my free time contributing to just about anything i find cool, and do plan to continue on astropy. For reference i'm an AI systems engineer with a focus on security research and debugging. I completely respect whatever your team decide, just figured I'd let you know.