Update tskit-book-theme

[benjeffery]

No description provided.

[benjeffery]

Needs a full check of the new HTML before merging.

[codecov]

Codecov Report

Merging #2793 (e76c559) into main (1ebf619) will decrease coverage by 0.53%.
The diff coverage is n/a.

❗ Current head e76c559 differs from pull request most recent head 3340c62. Consider uploading reports for the commit 3340c62 to get more accurate results

@@            Coverage Diff             @@
##             main    #2793      +/-   ##
==========================================
- Coverage   89.95%   89.43%   -0.53%     
==========================================
  Files          29       30       +1     
  Lines       29263    29264       +1     
  Branches     5697     5723      +26     
==========================================
- Hits        26324    26171     -153     
- Misses       1669     1822     +153     
- Partials     1270     1271       +1     

Flag	Coverage Δ
c-tests	86.40% <ø> (-0.10%)	⬇️
lwt-tests	80.13% <ø> (ø)
python-c-tests	67.04% <ø> (-0.07%)	⬇️
python-tests	99.02% <ø> (ø)

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see 6 files with indirect coverage changes

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[benjeffery]

Merging now, with the theme unpinned so we can update without touching tskit.