chore: use ftpmirror for GNU sources

See https://www.gnu.org/prep/ftp.html

Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>
(cherry picked from commit 8555e94)

Author: smira

grub/pkg.yaml

@@ -5,7 +5,7 @@ dependencies:
   - stage: base
 steps:
   - sources:
-      - url: https://ftp.gnu.org/gnu/grub/grub-{{ .grub_version }}.tar.xz
+      - url: https://ftpmirror.gnu.org/gnu/grub/grub-{{ .grub_version }}.tar.xz
         destination: grub.tar.xz
         sha256: "{{ .grub_sha256 }}"
         sha512: "{{ .grub_sha512 }}"

mtools/pkg.yaml

@@ -5,7 +5,7 @@ dependencies:
   - stage: base
 steps:
   - sources:
-      - url: https://ftp.gnu.org/gnu/mtools/mtools-{{ .mtools_version }}.tar.gz
+      - url: https://ftpmirror.gnu.org/gnu/mtools/mtools-{{ .mtools_version }}.tar.gz
         destination: mtools.tar.gz
         sha256: "{{ .mtools_sha256 }}"
         sha512: "{{ .mtools_sha512 }}"