bug#43556: OBS missing icons

[bdju]

guix (GNU Guix) ae144ec797cebf6f00f80177101020e92e8f2c47
OBS Studio - 25.0.8 (linux)

here is a screenshot of my OBS:
https://waifupaste.moe/raw/lDy

here is a screenshot from the website, what it should look like
https://obsproject.com/assets/images/OBSDemoApp2504.png

notice the missing plus and minus buttos for sources, missing icons to
the left of each source that would show which kind of source it is,
missing icons to the right of the source for toggling if they're showing
and so on