Fix outdated ContentsManager testing guidance

[terminalchai]

Summary

• replace the outdated jupyter_server.services.contents.tests module reference
• document that the ContentsManager test suites now live in ests/services/contents in the source tree
• clarify that custom backends should copy or adapt those tests instead of importing them from the installed package

Testing

• d:/project_contribution/.venv/Scripts/python.exe -m sphinx -b html -W -q docs/source docs/build/html docs/source/developers/contents.rst

Closes #394

[lresende]

LGTM

[Zsailer]

@terminalchai It appears this PR was submitted using an agent/AI assistance without closer review by you (a person)—this is evident by the top level comment having improper formatting when originally submitted. I've edited the comment to fix the styling.

While we don't discourage using agents/LLMs to aid in contributing to this repo (I've used them myself!), to protect our maintainers from the burden of reviewing a large volume of work without a human oversight, it's really important to us ask you (as part of our community) do your best to ensure you're reviewing your contributions personally when using these tools before submitting. As we begin to use these tools more, let's target the highest quality PRs—not just the code/documentation we submit, but also the PR comments we write so we have a high quality trail of discussion and history around why changes were made.

All that said, thank you for your contribution here! I appreciate you taking the time here to improve our docs.

[terminalchai]

@terminalchai It appears this PR was submitted using an agent/AI assistance without closer review by you (a person)—this is evident by the top level comment having improper formatting when originally submitted. I've edited the comment to fix the styling.

While we don't discourage using agents/LLMs to aid in contributing to this repo (I've used them myself!), to protect our maintainers from the burden of reviewing a large volume of work without a human oversight, it's really important to us ask you (as part of our community) do your best to ensure you're reviewing your contributions personally when using these tools before submitting. As we begin to use these tools more, let's target the highest quality PRs—not just the code/documentation we submit, but also the PR comments we write so we have a high quality trail of discussion and history around why changes were made.

All that said, thank you for your contribution here! I appreciate you taking the time here to improve our docs.

Thanks for the note, and for fixing the formatting. That’s fair feedback, and I appreciate you calling it out. I’ll make sure I review both the changes and the PR text more carefully before submitting future AI-assisted contributions.