This test was updated - and moved to TestNetworkProcessMemoryPressure in webkit.org/b/260256, and is now consistently timing out in GTK - possibly related to 260526, maybe not. Unable to shrink memory footprint of process below the kill thresold, Killed -> related errors in bots and locally. Also perhaps the nomenclature for the location of this test binary could be improved.
It is very possible this can be fixed by https://github.com/WebKit/WebKit/pull/28337.
Addressed in https://github.com/WebKit/WebKit/pull/28337