Disable navigation with keys for docs HTML theme

[bjlittle]

🚀 Pull Request

Description

This pull-request avoids the following diagnostic issued by pydata-sphinx-theme:

The default value for `navigation_with_keys` will change to `False` in the next release.
If you wish to preserve the old behavior for your site, set `navigation_with_keys=True`
in the `html_theme_options` dict in your `conf.py` file. Be aware that `navigation_with_keys = True`
has negative accessibility implications: https://github.com/pydata/pydata-sphinx-theme/issues/1492

Reference:

• pydata-sphinx-theme issue #1492
• sphinx HTML Theming.

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[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (a47fd34) 89.71% compared to head (69cbea7) 89.74%.
Report is 11 commits behind head on main.

Files	Patch %	Lines
lib/iris/_shapefiles.py	98.79%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5747      +/-   ##
==========================================
+ Coverage   89.71%   89.74%   +0.03%     
==========================================
  Files          90       91       +1     
  Lines       22815    22906      +91     
  Branches     5438     5458      +20     
==========================================
+ Hits        20468    20558      +90     
  Misses       1617     1617              
- Partials      730      731       +1     

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