Ensure .git/config is updated for forks

Normally when a project is created, `Projects::CreateService` attempts
to initialize a Git directory and update the `.git/config` to include
the human-readable project full path. However, for forks and project
imports, the repository is imported in a separate background task. As a
result, attempts to write to the `.git/config` directory will fail
unless the job has completed first.

To ensure we always update `.git/config` after the import is complete,
we call this update in `Project#after_import`.

Relates to https://gitlab.com/gitlab-org/gitaly/-/issues/2902

app/models/project.rb

@@ -1802,6 +1802,7 @@ class Project < ApplicationRecord
     after_create_default_branch
     join_pool_repository
     refresh_markdown_cache!
+    write_repository_config
   end
 
   def update_project_counter_caches

changelogs/unreleased/sh-update-git-config-for-forks.yml

+---
+title: Ensure .git/config is updated for forks
+merge_request: 35305
+author:
+type: fixed

spec/models/project_spec.rb

@@ -4663,6 +4663,7 @@ RSpec.describe Project do
       expect(project).to receive(:refresh_markdown_cache!)
       expect(InternalId).to receive(:flush_records!).with(project: project)
       expect(DetectRepositoryLanguagesWorker).to receive(:perform_async).with(project.id)
+      expect(project).to receive(:write_repository_config)
 
       project.after_import
     end