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/artifact/ncurses.yml

@@ -3,6 +3,10 @@ ncurses:
     license-files:
       - COPYING
   source:
+    type: filelist
+    url: 'https://ftp.gnu.org/gnu/ncurses/'
+    regex: '/href="(?<file>ncurses-(?<version>[^"]+)\.tar\.gz)"/'
+  source-mirror:
     type: filelist
     url: 'https://ftpmirror.gnu.org/gnu/ncurses/'
     regex: '/href="(?<file>ncurses-(?<version>[^"]+)\.tar\.gz)"/'