Disable unstable test (#12829)

Signed-off-by: Jacob Laursen <jacob-github@vindvejr.dk>

itests/org.openhab.binding.mqtt.homie.tests/src/main/java/org/openhab/binding/mqtt/homie/HomieImplementationTest.java

@@ -172,6 +172,7 @@ public class HomieImplementationTest extends MqttOSGiTest {
     }
 
     @SuppressWarnings("null")
+    @Disabled("Temporarily disabled: unstable")
     @Test
     public void retrieveAttributes() throws Exception {
         assertThat(homieConnection.hasSubscribers(), is(false));