Ensure that git repository is closed before transfer (#18049) (#18057)

Backport #18049

Repository Transfer requires that the repository directory is renamed - which
is not possible on Windows if the git repository is open.

Fix #17885

Signed-off-by: Andrew Thornton <art27@cantab.net>

routers/web/repo/repo.go

@@ -319,6 +319,11 @@ func acceptOrRejectRepoTransfer(ctx *context.Context, accept bool) error {
 	}
 
 	if accept {
+		if ctx.Repo.GitRepo != nil {
+			ctx.Repo.GitRepo.Close()
+			ctx.Repo.GitRepo = nil
+		}
+
 		if err := repo_service.TransferOwnership(repoTransfer.Doer, repoTransfer.Recipient, ctx.Repo.Repository, repoTransfer.Teams); err != nil {
 			return err
 		}