remote.c: specify correct plural form in "commit diverge" message

We need to count both "ours" and "theirs" commits when selecting plural form for this message. Note that even though in this block, both ours and theirs must be positive (i.e. can't be in singular form), we still keep Q_(singular, plural) because languages other than English may have more than one plural form. Reported-by: Alfonsogonzalez, Ernesto (GE Digital) <ernesto.alfonsogonzalez@ge.com> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>