systemd/gnome-shell-mobile: fix missing makedependency

The issue didn't exist locally or in CI because pmb already installed py3-docutils
as a makedependency of mutter-mobile

Part-of: https://gitlab.postmarketos.org/postmarketos/pmaports/-/merge_requests/6369

extra-repos/systemd/gnome-shell-mobile/APKBUILD

@@ -3,7 +3,7 @@
 pkgname=gnome-shell-mobile
 pkgver=99948.0
 _pkgver=48.0
-pkgrel=0
+pkgrel=1
 pkgdesc="GNOME shell mobile"
 url="https://wiki.gnome.org/Projects/GnomeShell"
 # gjs / riscv64: mutter-mobile
@@ -53,6 +53,7 @@ makedepends="
 	pipewire-dev
 	polkit-dev
 	pulseaudio-dev
+	py3-docutils
 	py3-setuptools
 	python3
 	sassc