temp/mutter-mobile: disable on riscv64

Fails for a weird reason, disable to get the initial bpo build for
riscv64 done.

Related: https://builds.sr.ht/~postmarketos/job/869829

temp/mutter-mobile/APKBUILD

@@ -5,7 +5,9 @@ pkgver=43.0
 pkgrel=1
 pkgdesc="clutter-based window manager and compositor"
 url="https://wiki.gnome.org/Projects/Mutter/"
-arch="all"
+# ricsv64: doesn't build currently:
+# https://builds.sr.ht/~postmarketos/job/869829#task-pmbootstrap_build-1224
+arch="all !riscv64"
 license="GPL-2.0-or-later"
 depends="
 	gnome-settings-daemon