winmm: Fix handle leak in timer tests.

dlls/winmm/tests/timer.c

@@ -190,6 +190,7 @@ static void test_priority(void)
            "thread priority is %s, should be THREAD_PRIORITY_TIME_CRITICAL\n",
            get_priority(priority));
     }
+    timeKillEvent(id);
 }
 
 START_TEST(timer)