Fix failing pkgdown

[VisruthSK]

Submission Checklist

• Run unit tests
• Declare copyright holder and agree to license (see below)

Summary

Fixes failing pkgdown GHA. Closes #1241. This is a temporary fix though and won't be needed when either package has a version bump/when their binaries are rebuilt for any reason.

Copyright and Licensing

Please list the copyright holder for the work you are submitting
(this will be you or your assignee, such as a university or company):
Visruth Srimath Kandali

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.71%. Comparing base (2989b3e) to head (5886f9a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1242      +/-   ##
==========================================
- Coverage   91.73%   91.71%   -0.02%     
==========================================
  Files          15       15              
  Lines        6277     6277              
==========================================
- Hits         5758     5757       -1     
- Misses        519      520       +1     

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[VisruthSK]

This run is green: https://github.com/stan-dev/cmdstanr/actions/runs/30764265176.

[jgabry]

Thanks. Should we keep this (or a different) issue open to remember to remove this special handling eventually?

[VisruthSK]

Yes, maybe keeping the same issue open and modifying it is good enough though, less churn.