Fix panic when branch.autosetuprebase is set (#5442)

### PR Description

It actually expect `branch.<name>.*`

`man git-config | rg "\s+branch\.\S+\$"` to show all possible keys.

```
panic: runtime error: slice bounds out of range [7:6]

goroutine 57 [running]:
github.com/jesseduffield/lazygit/pkg/commands/git_commands.(*ConfigCommands).Branches(0x110187428260, {0x15495d0, 0x110187190230})
        lazygit/pkg/commands/git_commands/config.go:104 +0x8ef
github.com/jesseduffield/lazygit/pkg/commands/git_commands.(*BranchLoader).Load(0x1101873e6180, {0x1d77440, 0x0, 0x0}, 0x1101873e86e0, {0x0, 0x0, 0x0}, 0x1, 0x1101872a5e60, 
...)
        lazygit/pkg/commands/git_commands/branch_loader.go:121 +0x7cc
github.com/jesseduffield/lazygit/pkg/gui/controllers/helpers.(*RefreshHelper).refreshBranches(0x1101871ef1c0, 0x1, 0x0, 0x1)
        lazygit/pkg/gui/controllers/helpers/refresh_helper.go:456 +0x328
github.com/jesseduffield/lazygit/pkg/gui/controllers/helpers.(*RefreshHelper).Refresh.func2.3()
        lazygit/pkg/gui/controllers/helpers/refresh_helper.go:131 +0x45
github.com/jesseduffield/lazygit/pkg/gui/controllers/helpers.(*RefreshHelper).Refresh.func2.1.1({0x154b438, 0x110187b12260})
        lazygit/pkg/gui/controllers/helpers/refresh_helper.go:106 +0x30
github.com/jesseduffield/gocui.(*Gui).onWorkerAux(0x110187278b40, 0x110187a92190, {0x154b438, 0x110187b12260})
        lazygit/vendor/github.com/jesseduffield/gocui/gui.go:713 +0x8b
github.com/jesseduffield/gocui.(*Gui).OnWorker.func1()
        lazygit/vendor/github.com/jesseduffield/gocui/gui.go:700 +0x3f
created by github.com/jesseduffield/gocui.(*Gui).OnWorker in goroutine 1
```

### Please check if the PR fulfills these requirements

* [x] Cheatsheets are up-to-date (run `go generate ./...`)
* [x] Code has been formatted (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#code-formatting))
* [ ] Tests have been added/updated (see
[here](https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md)
for the integration test guide)
* [x] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
* [x] If a new UserConfig entry was added, make sure it can be
hot-reloaded (see
[here](https://github.com/jesseduffield/lazygit/blob/master/docs/dev/Codebase_Guide.md#using-userconfig))
* [x] Docs have been updated if necessary
* [x] You've read through your own file changes for silly mistakes etc

pkg/commands/git_commands/config.go

@@ -93,7 +93,8 @@ func (self *ConfigCommands) Branches(cmd oscommands.ICmdObjBuilder) map[string]*
 		}
 		// key is like "branch.<name>.remote" or "branch.<name>.merge"
 		lastDot := strings.LastIndex(key, ".")
-		if lastDot < 0 {
+		// ignore key like branch.autosetuprebase
+		if lastDot < len("branch.") {
 			continue
 		}
 		configKey := key[lastDot+1:]