git maintenance: avoid console window in scheduled tasks on Windows

We just introduced a helper to avoid showing a console window when the
scheduled task runs `git.exe`. Let's actually use it.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/gc.c

@@ -2068,7 +2068,7 @@ static int schtasks_schedule_task(const char *exec_path, enum schedule_priority
 	      "</Settings>\n"
 	      "<Actions Context=\"Author\">\n"
 	      "<Exec>\n"
-	      "<Command>\"%s\\git.exe\"</Command>\n"
+	      "<Command>\"%s\\headless-git.exe\"</Command>\n"
 	      "<Arguments>--exec-path=\"%s\" for-each-repo --config=maintenance.repo maintenance run --schedule=%s</Arguments>\n"
 	      "</Exec>\n"
 	      "</Actions>\n"