fetch: fix failed batched updates skipping operations
Fix a regression introduced with batched updates in 0e358de64a (fetch: use batched reference updates, 2025-05-19) when fetching references. In the `do_fetch()` function, we jump to cleanup if committing the transaction fails, regardless of whether using batched or atomic updates. This skips three subsequent operations: - Update 'FETCH_HEAD' as part of `commit_fetch_head()`. - Add upstream tracking information via `set_upstream()`. - Setting remote 'HEAD' values when `do_set_head` is true. For atomic updates, this is expected behavior. For batched updates, we want to continue with these operations even if some refs fail to update. Skipping `commit_fetch_head()` isn't actually a regression because 'FETCH_HEAD' is already updated via `append_fetch_head()` when not using '--atomic'. However, we add a test to validate this behavior. Skipping the other two operations (upstream tracking and remote HEAD) is a regression. Fix this by only jumping to cleanup when using '--atomic', allowing batched updates to continue with post-fetch operations. Add tests to prevent future regressions. Helped-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Karthik Nayak <karthik.188@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>