styles: Fix unintended color in builder-dark and wrong metadata in peninsula-dark

Merged Vanya Nartov requested to merge piousdeer/gnome-builder:styles-fixes into main

Although #orange3 is successfully parsed by Gdk, nowhere else in the official style schemes color names are prefixed with #, so I assume it's a mistake. I went with orange2 because it's closer to the current color and isn't considerably darker than the element name, unlike orange3.

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