Do not add HTML mixin if not building html

[simonspa]

When attempting to build the latexpdf target, pydata-sphinx-theme 0.16 currently fails on Sphinx 8.1.3 with:

Exception occurred:
  File "/home/simonspa/venv/lib64/python3.13/site-packages/pydata_sphinx_theme/translator.py", line 41, in visit_table
    self._table_row_indices.append(0)
    ^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'BootstrapHTML5Translator' object has no attribute '_table_row_indices'
The full traceback has been saved in /tmp/sphinx-err-7w3z72wv.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
make: *** [Makefile:25: latexpdf] Error 1

The issue appears to be that the BootstrapHTML5Mixin is added despite the target not being html. This PR moves the check for app.builder.format to the top level of setup_translators.

(cc) @stephanlachnit

[gabalafou]

This change makes sense to me, but just FYI, I am unable to reproduce the bug.

Using:

• my own small example docs repo (which has a RST table)
• Sphinx 8.1.3
• PyData Sphinx Theme 0.16.0
• Python 3.13

I ran make latexpdf but I did not get any errors.

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
src/pydata_sphinx_theme
translator.py					88
Project Total

This report was generated by python-coverage-comment-action

[drammock]

I recommend waiting to merge until after 0.16.1 is out. This seems innocuous but I would hate to break a bunch of user sites and have to scramble to cut a _post release in a hurry.

[gabalafou]

@drammock, agreed

[simonspa]

@gabalafou thanks to your minimal example I was able to find my mistake: I listed the pydata_sphinx_theme also under extensions, not only as html theme.

I anyway think the fix makes sense. :)