webp generation fails on Linux with Pillow 9.5.0 (key error) incl. workaround

[derfasthirnlosenick]

Hi!

Might be specific to my system, but in case this affects more people, here's my workaround/ suggestion for a potential fix.

I had issues with generating WEBP files (if selected as an output/preview format, or as the thumbnail of the infinite image browser extension), resulting in a key error.

Apart from installing libwebp-dev (system package via apt) I had to update Pillow to 10.4.0 to get it working.

As forge would check the requirements file and downgrade pillow to 9.5.0 on every start, I am now using the --skip-install flag (rather than editing the requirements, as that messes with the git pull I run on every start).

So far, I haven't experienced any issues running the new version of Pillow, so it might be worth just updating the version in the requirements file.

Sidenote: Forge has hardcoded versions on every package except pytorch, base Webui has far fewer (protobuf for one), so version updates could probably be done on other packages as well.