testing/skribilo: add explicit dependency on guile-reader

Since skribilo does not link against guile reader but instead loads the
.so via the guile FFI abuild is not able to infer this dependency.

testing/skribilo/APKBUILD

@@ -2,12 +2,12 @@
 # Maintainer: Sören Tempel <soeren+alpine@soeren-tempel.net>
 pkgname=skribilo
 pkgver=0.9.5
-pkgrel=0
+pkgrel=1
 pkgdesc="A free document production tool for structured documents"
 url="https://www.nongnu.org/skribilo"
 arch="all"
 license="GPL-3.0-or-later"
-depends="guile imagemagick"
+depends="guile guile-reader imagemagick"
 makedepends="guile-dev guile-reader-dev"
 subpackages="$pkgname-dev $pkgname-doc"
 options="!strip" # https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=907061