git init fails because of includeIf configuration

Thank you for filling out a Git bug report! Please answer the following questions to help us understand your issue.

What did you do before the bug happened? (Steps to reproduce your issue)

I have a section of configuration for specific branch in my ~/.gitconfig file. It looks like this

```
[includeIf "onbranch:other"]
         path=~/.gitconfig-other
```

In ~/.gitconfig-other I have this (the values are changed)

```
[user]
     email = myemail@email.com
     name = My Name
     signingkey = KEYID

[commit]
     gpgsign = true

[credential]
     username = username
```

I ran `git init` in empty directory.

What did you expect to happen? (Expected behavior)

Initialize repository with or without includeIf configuration section.

What happened instead? (Actual behavior)

```
$ git init
BUG: refs.c:2123: reference backend is unknown
zsh: IOT instruction (core dumped)  git init
```

What's different between what you expected and what actually happened?

I have expected to initialize a new repository but got an error message.

Anything else you want to add:

I ended up commenting includeIf section in my .gitconfig file, initialize repository then uncomment that section and use git as usual. The problem might be related only to `git init`.

Please review the rest of the bug report below. You can delete any lines you don't wish to share.

[System Info] git version: git version 2.45.2 cpu: x86_64 no commit associated with this build sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh uname: Linux 6.6.34-1-lts #1 SMP PREEMPT_DYNAMIC Sun, 16 Jun 2024 14:45:31 +0000 x86_64 compiler info: gnuc: 14.1 libc info: glibc: 2.39 $SHELL (typically, interactive shell): /bin/zsh

[Enabled Hooks] not run from a git repository - no hooks to show