For some reason when branch from V2 models is being saved, it tries to
also update relationships for V3 models, at least in tests. This fails,
because default_branch association on the V3 Repository model has a
primary key set to [:id, :default_branch]. In theory we use composite
keys plugin, but it seems that it doesn't cover that case and because of
that AR fails with an error "[:id, :default_branch] is not a Symbol"
when it tries to call Model#send with primary_key as an argument.
This commit fixes the issue by overriding the send method on the
Repository model to not fail when AR does
repository.send([:id, :default_branch_name]), when it needs to fetch
a primary key.
This is hacky, but I haven't found a nicer way to get around it.
