Re: [PATCH v2 20/21] environment: stop storing "core.warnAmbiguousRefs" globally

> Same as the preceding commits, storing the "core.warnAmbiguousRefs"
> value globally is misdesigned as this setting may be set per repository.
>
> Move the logic into the repo-settings subsystem. The usual pattern here
> is that users are expected to call `prepare_repo_settings()` before they
> access the settings themselves. This seems somewhat fragile though, as
> it is easy to miss and leads to somewhat ugly code patterns at the call
> sites.
>
> Instead, introduce a new function that encapsulates this logic for us.
> This also allows us to change how exactly the lazy initialization works
> in the future, e.g. by only partially initializing values as requested
> by the caller.