Using LOCAL_MIRROR=true fails in restructured branch

[petefoth]

21.0 build, using the pf_restructure-build branch, ssing LOCAL_MIRROR=true` fails with the following error

>> [Tue Sep  3 13:12:30 UTC 2024] Syncing mirror repository
repo sync has finished successfully.
>> [Tue Sep  3 13:21:20 UTC 2024] (Re)initializing branch repository
warning: Changing --git-lfs settings will only affect new project checkouts.
         Existing projects will require manual updates.

fatal: manifest 'default.xml' not available
fatal: remote github already exists with different attributes
================================================================================
Repo command failed: UpdateManifestError
        Unable to sync manifest default.xml
repo: reusing existing repo client checkout in /srv/mirror
>> [Tue Sep  3 13:23:51 UTC 2024] (Re)initializing branch repository
warning: Changing --git-lfs settings will only affect new project checkouts.
         Existing projects will require manual updates.

Originally posted by @petefoth in #678 (comment)