chore: still keep ctx in git.Repository struct for cat-file batch command (#38684)

Unfortunately, we can't completely remove the ctx from git.Repository,
because the CatFileBatch still heavily depends on a parent context.

If we remove the Repository ctx, the CatFileBatch will become a mess and
create a lot of unnecessary git processes.

http://localhost:3000/-/admin/monitor/perftrace

* Before: open a repo home, dozens of git processes (duplicate cat-file)
* After: only a few (no duplicate cat-file)

modelmigration/v1_14/v156.go

@@ -97,7 +97,7 @@ func FixPublisherIDforTagReleases(ctx context.Context, x base.EngineMigration) e
 						return err
 					}
 				}
-				gitRepo, err = git.OpenRepository(base.LocalCodeGitRepo(repo.OwnerName, repo.Name))
+				gitRepo, err = git.OpenRepository(ctx, base.LocalCodeGitRepo(repo.OwnerName, repo.Name))
 				if err != nil {
 					log.Error("Error whilst opening git repo for [%d]%s/%s. Error: %v", repo.ID, repo.OwnerName, repo.Name, err)
 					return err

modelmigration/v1_9/v82.go

@@ -85,7 +85,7 @@ func FixReleaseSha1OnReleaseTable(ctx context.Context, x base.EngineMigration) e
 					userCache[repo.OwnerID] = user
 				}
 
-				gitRepo, err = git.OpenRepository(base.LocalCodeGitRepo(user.Name, repo.Name))
+				gitRepo, err = git.OpenRepository(ctx, base.LocalCodeGitRepo(user.Name, repo.Name))
 				if err != nil {
 					return err
 				}