The idea is to make it easier and more obvious how to get the runtime GTK+/GLib versions. I'm not sure it adds much over the Debug Messages window except that the textbox can get quite long to scroll and its contents can be cleared.
Since I already made the patch, I figured I'd add a PR for it.
Feel free to close, I'm rather indifferent on it. You can view, comment on, or merge this pull request online at:
https://github.com/geany/geany/pull/2163
-- Commit Summary --
* Show the GTK/GLib versions in about dialog
-- File Changes --
M src/about.c (17)
-- Patch Links --
https://github.com/geany/geany/pull/2163.patch https://github.com/geany/geany/pull/2163.diff