git init BUG when gitconfig has includeIf

[Heghedus Razvan <heghedus.razvan@protonmail.com>]

Hello everybody

Yesterday I stumble upon a bug when doing git init. I didn't
find any references to it, so I don't know if is a known problem
or not.

Steps to reproduce:
# git init .
BUG: refs.c:2123: reference backend is unknown

I'm able to reproduce this on multiple systems where the git
version is newer than v2.44.0. This happens only when I have
an "includeIf" in the ~/.gitconfig . Bellow [1] I have a
minimal configuration for reproducing the bug. With same
gitconfig but versions lower than v2.43.4 the error is
no longer happening.

So I went and did a git bisection and the error appeared with
173761e21b setup: start tracking ref storage format
Previous commit ("0fcc285c5e") is working fine.

I cc'ed Patrick Steinhardt since the error appeared from his
commit.

Best regards,
Razvan

--

1:
content of ~/.gitconfig
```
[user]
        email = some_email@test.net
        name = test
[includeIf "onbranch:upstream*"]
        path=~/.gitconfig_upstream
```

content of ~/.gitconfig_upstream
```
[user]
        name = test test
```