[tests] Fix unit tests timed out

The debug-tests was changing the compilation (TINY_MQTT_DEBUG on)
Thus the other tests were too long to execute due to Serial output emulation.

tests/debug-mode/debug-tests.ino

@@ -0,0 +1,15 @@
+#include <Arduino.h>
+#include <AUnit.h>
+#include <TinyMqtt.h>
+#include <map>
+#include <iostream>
+#include <iomanip>
+#include <sstream>
+#include <string>
+
+// Only compilation check, so do nothing
+
+void setup() {}
+void loop() {
+  aunit::TestRunner::run();
+}