- `GetSubModules` already solely stores the URL of the submodule and not
a `*SubModule` entry, so don't try to type assert it to be a struct.
- I am not able to pinpoint when this was regressed but if I had to
guess it might be #4941.
- Added integration test.
(cherry picked from commit e7cffc378fe8dd3b77959ad318483e829013726a)