templates: Use GApplication runAsync for GJS

Merged Sonny Piers requested to merge (removed):runAsync into main

Replaces the workaround introduced in !632 (merged)

runAsync is a GJS only API and was introduced in GNOME 44 / GJS 1.75.2


This has been tested, but it would be cool if @ewlsh or @ptomato could 👍

Merge request reports