git: update to v2.21.0

Update to git version v2.21.0. Required changes follow upstream commits:

* 6a7895fd8a3bd409f2b71ffc355d5142172cc2a0
  (commit: prepare free_commit_buffer and release_commit_memory for
  any repo)

* e092073d643b17c82d72cf692fbfaea9c9796f11
  (tree.c: make read_tree*() take 'struct repository *')

Signed-off-by: Christian Hesse <mail@eworm.de>
Reviewed-by: John Keeping <john@keeping.me.uk>

1 files changed, 0 insertions, 0 deletions

diff --git a/git b/git
-Subproject 5d826e972970a784bd7a7bdf587512510097b8c
+Subproject 8104ec994ea3849a968b4667d072fedd1e68864