main/postmarketos-artwork: fix upgrade failure with -gnome subpackage (MR 5031)

This subpackage now installs a file that was previously in the other
subpackage it is meant to replace, leading to upgrade conflicts that
have to be manually resolved (i.e. with apk fix)

Fixes: 126f4322 and 1712a2d0

main/postmarketos-artwork/APKBUILD

 # Maintainer: Oliver Smith <ollieparanoid@postmarketos.org>
 pkgname=postmarketos-artwork
 pkgver=5
-pkgrel=1
+pkgrel=2
 pkgdesc="Meta package for the postmarketOS artwork"
 url="https://postmarketos.org/"
 arch="noarch"
@@ -73,6 +73,7 @@ wallpapers_extra() {
 
 wallpapers_gnome() {
 	pkgdesc="Wallpaper configuration for GNOME-based UIs"
+	replaces="postmarketos-base-ui-gnome-wallpaper-pmos"
 	install_if="postmarketos-artwork-wallpapers=$pkgver-r$pkgrel postmarketos-base-ui-gnome"
 
 	install -Dm644 "$srcdir"/postmarketos-gnome.xml \