fetch: silence git-gc if --quiet is given

Noticed-by: Matthew Flaschen <mflaschen@wikimedia.org>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -1197,6 +1197,8 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	string_list_clear(&list, 0);
 
 	argv_array_pushl(&argv_gc_auto, "gc", "--auto", NULL);
+	if (verbosity < 0)
+		argv_array_push(&argv_gc_auto, "--quiet");
 	run_command_v_opt(argv_gc_auto.argv, RUN_GIT_CMD);
 	argv_array_clear(&argv_gc_auto);