The test in question moves the mouse pointer to the top left corner of an input element and tries to click, but on GTK/WPE this misses if the system theme results in the element having rounded corners, meaning the top left corner of the bounding box is not actually inside the element. It should move the mouse to the center instead.
Created attachment 435092 [details]
For what it's worth a quick search of other tests that use eventSender.mouseMoveTo with offsetLeft shows that the overwhelming majority use some kind of offset, presumably because of exactly this sort of issue.
Committed r280779 (240363@main): <https://commits.webkit.org/240363@main>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 435092 [details].