Switch to using mirror emacs-mirror/emacs on github

[djgoku]

Maybe switch to github emacs mirror to fix issues like #460

Not sure if this is a welcome PR if not please close it.

% ./update emacs                    
+++ dirname repos/emacs/update
++ cd repos/emacs
++ pwd -P
+ SCRIPTPATH=~/dev/github/djgoku/emacs-overlay/repos/emacs
+ cd ~/dev/github/djgoku/emacs-overlay/repos/emacs
+ update_savannah_branch master
+ branch=master
+ echo emacs master
emacs master
++ curl https://github.com/emacs-mirror/emacs/commits/master.atom
++ xmlstarlet sel -N atom=http://www.w3.org/2005/Atom -t -m /atom:feed/atom:entry -v 'concat(atom:id,'\''/'\'',atom:updated)' -n
++ head -n 1
++ sed 's/^tag:github.com,2008:Grit::Commit\///'
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 21351  100 21351    0     0  58934      0 --:--:-- --:--:-- --:--:-- 58980
+ commit_data=92c5c1b786968b6d80f5d27455a40443a3a8f0e8/2025-01-22T23:07:36Z
++ echo 92c5c1b786968b6d80f5d27455a40443a3a8f0e8/2025-01-22T23:07:36Z
++ cut -d / -f 1
+ commit_sha=92c5c1b786968b6d80f5d27455a40443a3a8f0e8
++ echo 92c5c1b786968b6d80f5d27455a40443a3a8f0e8/2025-01-22T23:07:36Z
++ cut -d / -f 2
++ cut -d T -f 1
++ sed s/-//g
+ version_number=20250122.0
++ echo master
++ sed 's/\//_/'
+ output_branch=master
++ nix-prefetch-url --unpack https://github.com/emacs-mirror/emacs/archive/92c5c1b786968b6d80f5d27455a40443a3a8f0e8.tar.gz
path is '/nix/store/5f2ql8ky8ghwyhqqclr9fzb1hmvw9ix5-92c5c1b786968b6d80f5d27455a40443a3a8f0e8.tar.gz'
+ digest=0ahia6jndl20sczzl40ndqs0bj6ddmczqsmq7cghsdh3j53mzign
+ echo '{"type": "github", "owner": "emacs-mirror", "repo": "emacs", "rev": "92c5c1b786968b6d80f5d27455a40443a3a8f0e8", "sha256": "0ahia6jndl20sczzl40ndqs0bj6ddmczqsmq7cghsdh3j53mzign", "version": "20250122.0"}'
[feat/maybe-use-github-emacs-mirror-of-emacs 1abbfcbdc] Updated emacs
 2 files changed, 8 insertions(+), 8 deletions(-)

[djgoku]

I had another idea (although this might not be desired). We could create a function is_savannah_repo_type that returns 0 if REPO_TYPE is savannah or not set, and 1 if REPO_TYPE is github. This would enable us to support both types.

[adisbladis]

I don't know who maintains the Github Emacs mirror and think it's generally better that we use Savannah.
In case of temporary hickups you should be able to access sources mirrored in the nix-community cache.

[djgoku]

Ahh. Good call out on not knowing who maintains emacs-mirror. This might be a better one that could be a backup. https://github.com/emacsmirror/emacs this is maintained my (originally had John wrigley) Jonas Bernoulli.

Thanks for this repository too!