btrfs: test snapshotting a subvolume that was just created

btrfs: test snapshotting a subvolume that was just created

Test that snapshotting a new subvolume (created in the current transaction)
that has a btree with a height > 1, works and does not result in a fs
corruption.

This exercises a regression introduced in kernel 6.5 by the kernel commit:

  1b53e51a4a8f ("btrfs: don't commit transaction for every subvol create")

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>