Switch numpy pin to lower bound in docs

[brynpickering]

Closes #872

Docs build locally so I assume this upper bound was a legacy that's no longer required.

Checklist

• AI-generated content is marked (see AGENTS.md).
• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[codspeed-hq]

Merging this PR will not alter performance

✅ 175 untouched benchmarks
⏩ 175 skipped benchmarks¹

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_{Comparing fix/numpy-version-docs (a8cf78a) with master (f268bff)}

Footnotes

1. 175 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[FBumann]

Already in #869

[brynpickering]

Noted @FBumann. Would be good to have PRs linked to issues so these dups don't occur.

[FBumann]

Yes! But my pr was there before your issue :)