guix system image: unexpected guix pull from savannah

[Vasilii Smirnov]

Hello, people. So, today savannah is down for some reason, which
prompted me to switch to a local guix mirror:

> $ guix describe
> Generation 27      Jun 25 2024 21:31:53    (current)
>   guix 43e102b
>     repository URL: /home/user/Projects/guix
>     branch: master
>     commit: 43e102be746e5be11ddd9e1af9b65e3d8571d232

After this I checked "guix pull" and "guix system reconfigure" - they
worked fine. But then I tried creating an installation image and it
failed trying to pull from savannah again:

> $ guix system image --image-type=iso9660 --fallback installer.scm
> Updating channel 'guix' from Git repository at 
> 'https://git.savannah.gnu.org/git/guix.git'...
> Backtrace:
> In guix/gexp.scm:
>     913:4 19 (_ _)
> In guix/store.scm:
>   2090:12 18 (_ #<store-connection 256.100 7ff670c46280>)
>   1407:11 17 (map/accumulate-builds #<store-connection 256.100 7ff6…> …)
>    1325:8 16 (call-with-build-handler #<procedure 7ff66ffa97b0 at g…> …)
>   2205:25 15 (run-with-store #<store-connection 256.100 7ff670c46280> …)
> In guix/gexp.scm:
>    918:13 14 (_ _)
> In guix/store.scm:
>    2033:8 13 (_ _)
> In guix/gexp.scm:
>    299:22 12 (_ _)
> In guix/store.scm:
>    2033:8 11 (_ _)
> In guix/gexp.scm:
>    299:22 10 (_ _)
> In guix/store.scm:
>    2033:8  9 (_ _)
> In guix/packages.scm:
>   2010:11  8 (_ _)
> In guix/build-system/channel.scm:
>      43:2  7 (_ _)
> In guix/store.scm:
>   2077:38  6 (_ #<store-connection 256.100 7ff670c46280>)
> In guix/channels.scm:
>    559:23  5 (latest-channel-instances #<store-connection 256.100 7…> …)
>    422:18  4 (latest-channel-instance #<store-connection 256.100 7f…> …)
> In guix/git.scm:
>     541:7  3 (update-cached-checkout _ #:ref _ #:recursive? _ # _ # _ …)
> In git/bindings.scm:
>      77:2  2 (raise-git-error _)
> In ice-9/boot-9.scm:
>   1685:16  1 (raise-exception _ #:continuable? _)
>   1685:16  0 (raise-exception _ #:continuable? _)
> 
> ice-9/boot-9.scm:1685:16: In procedure raise-exception:
> Git error: failed to connect to git.savannah.gnu.org: Network is unreachable

Does anyone know why it does that? Any way to fix this?