promisor-remote.h: include missing header

When we ran `make hdr-check`, we got the following warning message: promisor-remote.h:21:46: warning: declaration of 'struct repository' will not be visible outside of this function [-Wvisibility] extern int promisor_remote_get_direct(struct repository *repo, ^ 1 warning generated. This was caused by a missing reference to `struct repository`, which is defined in "repository.h". Include this missing header to fix this warning. Signed-off-by: Denton Liu <liu.denton@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>