Manifest repo 不再默认 Track main，导致 mono sync 报错

Summary

Mono client 问题版本：v3.1.0

Bug 引自：!17 (merged) 。

Steps to reproduce

1. 按 安装步骤 完成 Mono client 的安装
2. 执行 mono sync 会遇到报错

$ mono sync
fatal: Couldn't find remote ref refs/heads/main-jh
manifests: sleeping 4.0 seconds before retrying
fatal: the remote end hung up unexpectedly
remote: 
remote: ========================================================================
remote: 
remote: ERROR: user canceled the fetch

remote: 
remote: ========================================================================
remote: 
fatal: Couldn't find remote ref refs/heads/main-jh
error: in `sync`: revision refs/heads/main-jh in manifests not found
Deer@Deer-PC:~/Mono/test-bug-of-3.0.1-track-main$ fatal: the remote end hung up unexpectedly
remote: 
remote: ========================================================================
remote: 
remote: ERROR: user canceled the fetch

remote: 
remote: ========================================================================
remote: 

What is the current bug behavior?

在执行 mono sync 总是报错。

Possible fixes

diff --git a/project.py b/project.py
index 8b54715..d2448e7 100644
--- a/project.py
+++ b/project.py
@@ -4372,7 +4372,7 @@ class ManifestProject(MetaProject):
             syncbuf.Finish()
 
             if is_new or self.CurrentBranch is None:
-                if not self.StartBranch("default"):
+                if not self.StartBranch("default", branch_merge=manifest_branch):
                     print(
                         "fatal: cannot create default in manifest",
                         file=sys.stderr,