bug#43221: webkitgtk fails to build on aarch64

[Vitaliy Shatrov]

Hello Guixes.

OK, picture:  webkitgtk has propagated-input  libsoup
              libsoup has   native-input      php

The libsoup builds fine, but one of its tests (performed by php) fails.
So webkitgtk is unavailable on aarch64.

Bye.