excluding the `.png` icons.
this also fixes the wrong `.patch` and `.diff` extensions checks.
no clue why we were trying to find `.patch` and `.diff` to begin with.
i think i probably copy pasted the command i tested on nsxiv-extra repo
or somewhere else without changing the extensions to `.c` and `.h`.
Reviewed-on: https://codeberg.org/nsxiv/nsxiv/pulls/345