Use only time.windows.com in SNTP test

test/unit_test.c

@@ -325,7 +325,9 @@ static void test_sntp_server(const char *url) {
 
 static void test_sntp(void) {
   test_sntp_server("udp://time.windows.com:123");
-  test_sntp_server(NULL);
+  // NOTE(cpq): temporarily disabled until Github Actions fix their NTP
+  // port blockage issue, https://github.com/actions/runner-images/issues/5615
+  // test_sntp_server(NULL);
 
   {
     int64_t ms;