PDF generation is broken when a page has images in WebP format

[kartben]

Describe the bug

As part of #60204, a documentation page that includes images in WebP format was introduced.
LaTeX does not allow WebP images to be included and as a result the generation of the documentation in PDF format fails.

To Reproduce

cd ~/zephyrproject/zephyr/doc
rm _build -Rf && cmake -GNinja -B_build . -DDT_TURBO_MODE=1 && cd _build && ninja latex

Expected behavior

Build succeeds and WEBP images (or their equivalent in another supported format) are correctly embedded in the PDF.

Impact

PDF available at https://docs.zephyrproject.org/latest/zephyr.pdf is incomplete

Additional context

The following PR would allow us to properly instruct Sphinx to convert WebP files to PNG prior to building the PDF
sphinx-doc/sphinx#12224

[kartben]

As sphinx-doc/sphinx#12224 has been merged, PDF generation should be working again as soon as a new Sphinx release is out 🤞🏼

[github-actions]

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[kartben]

Fixed in Sphinx upstream