[bug#46113] [PATCH] gnu: obs: Update obs to fb347c.

[Andrew Tropin]

It's a commit from master branch containing changes from PR:
https://github.com/obsproject/obs-studio/pull/4067

It's just few commits after 26.1.2 and it seems there is no any big
changes since that and should be safe to use.

I asked for 26.1.3 tag, but it seems that it won't happen in nearest
future: https://github.com/obsproject/obs-studio/issues/4100

As one of developers said to me, usually obs releases once in 3-4
months, that is why I decided to use a commit instead of tag.

The changes is needed to be able to specify plugin load path using
native-search-paths to be able to package obs plugins with guix.