[BUG] fatal: expected flush after ref listing

I use this tool for git clone, which met a bug: 

```
$ git-http-backend --project_root=. --git_bin_path=/home/adl/git/bin-wrappers/git
$ git clone http://localhost:8080/mono-repo.git 
Cloning into 'mono-repo'...
fatal: expected flush after ref listing
```

system: Linux adl 6.0.8-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 10 Nov 2022 21:14:24 +0000 x86_64 GNU/Linux
git version: 2.38.1
