TST: unmaintained action using deprecated node.js

[neutrinoceros]

Bug report

Bug summary

the check-manifest stage of our wheels workflow is emitting a deprecation warning:

[Check MANIFEST.in](https://github.com/yt-project/yt/actions/runs/4245064745/jobs/7380072693)
Node.js 12 actions are deprecated. Please update the following actions to use Node.js 16: snickerbockers/submodules-init@v4. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/.

I'd normally report upstream (https://github.com/snickerbockers/submodules-init) but the repo seems very much abandoned.
It's possible that this action is actually unneeded and superseded by `actions/checkout, so I'll try cleaning it up.