fix(source): use ftp.gnu.org as primary, ftpmirror.gnu.org as fallback

All GNU packages now use ftp.gnu.org (stable canonical server) as the
primary filelist source, with ftpmirror.gnu.org configured as
source-mirror fallback. ftpmirror uses DNS round-robin across many
mirrors of varying reliability; this setup eliminates random CI failures
caused by unreachable mirror nodes while preserving a fallback path.

config/pkg/lib/gettext.yml

@@ -2,6 +2,10 @@ gettext:
   type: library
   artifact:
     source:
+      type: filelist
+      url: 'https://ftp.gnu.org/gnu/gettext/'
+      regex: '/href="(?<file>gettext-(?<version>[^"]+)\.tar\.xz)"/'
+    source-mirror:
       type: filelist
       url: 'https://ftpmirror.gnu.org/gnu/gettext/'
       regex: '/href="(?<file>gettext-(?<version>[^"]+)\.tar\.xz)"/'