setup: fix bug with "includeIf.onbranch" when initializing dir

setup: fix bug with "includeIf.onbranch" when initializing dir

It was reported that git-init(1) can fail when initializing an existing
directory in case the config contains an "includeIf.onbranch:"
condition:

    $ mkdir repo
    $ git -c includeIf.onbranch:main.path=nonexistent init repo
    BUG: refs.c:2056: reference backend is unknown

The same error can also be triggered when re-initializing an already
existing repository.

The bug has been introduced in 173761e21b (setup: start tracking ref
storage format, 2023-12-29), which wired up the ref storage format. The
root cause is in `init_db()`, which tries to read the config before we
have initialized `the_repository` and most importantly its ref storage
format. We eventually end up calling `include_by_branch()` and execute
`refs_resolve_ref_unsafe()`, but because we have not initialized the ref
storage format yet this will trigger the above bug.

Interestingly, `include_by_branch()` has a mechanism that will only
cause us to resolve the ref when `the_repository->gitdir` is set. This
is also the reason why this only happens when we initialize an already
existing directory or repository: `gitdir` is set in those cases, but
not when creating a new directory.

Now there are two ways to address the issue:

  - We can adapt `include_by_branch()` to also make the code conditional
    on whether `the_repository->ref_storage_format` is set.

  - We can shift around code such that we initialize the repository
    format before we read the config.

While the first approach would be safe, it may also cause us to paper
over issues where a ref store should have been set up. In our case for
example, it may be reasonable to expect that re-initializing the repo
will cause the "onbranch:" condition to trigger, but we would not do
that if the ref storage format was not set up yet. This also used to
work before the above commit that introduced this bug.

Rearrange the code such that we set up the repository format before
reading the config. This fixes the bug and ensures that "onbranch:"
conditions can trigger.

Reported-by: Heghedus Razvan <heghedus.razvan@protonmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Tested-by: Heghedus Razvan <heghedus.razvan@protonmail.com>
[jc: fixed a test and backported to v2.44.0 codebase]
Signed-off-by: Junio C Hamano <gitster@pobox.com>