maintenance(geometric): do release the `.idx` files before repacking
As is done for all the other maintenance tasks, let's release the ODB also before starting the geometric repacking. That way, the `.idx` files won't be `mmap()`ed when they are to be deleted (which does not work on Windows because you cannot delete files on that platform as long as they are kept open by a process). This regression was introduced by 9bc151850c1c (builtin/maintenance: introduce "geometric-repack" task, 2025-10-24), but was only noticed once geometric repacking was made the default in 452b12c2e0fe (builtin/ maintenance: use "geometric" strategy by default, 2026-02-24). The fix recapitulates my work from df76ee7b77f0 (run-command: offer to close the object store before running, 2021-09-09) & friends. To guard against future regressions of this kind, add a check to `run_and_verify_geometric_pack()` in `t7900` that detects orphaned `.idx` files left behind after repacking. Contrary to interactive calls, the `git maintenance` call in that test case would _not_ block on Windows, asking whether to retry deleting that file, which is the reason why this bug was not caught earlier. Furthermore, since the default behavior of `DeleteFileW()` was changed at some point between Windows 10 Build 17134.1304 and Build 18363.657 to use POSIX semantics (see https://stackoverflow.com/a/60512798), the added orphaned-`.idx` check would be insufficient to catch this regression on modern Windows without emulating legacy delete semantics via `GIT_TEST_LEGACY_DELETE=1`. This fixes https://github.com/git-for-windows/git/issues/6210. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>