Reduce sleep interval duration for thread that listens for messages

This seems to make the test pass more deterministically
If this value is higher than the one used for sending output (50ms) some messages may be lost
leading to failed test

ingestion/src/test/java/feast/ingestion/transform/metrics/WriteFeatureValueMetricsDoFnTest.java

@@ -281,7 +281,10 @@ public DummyStatsDServer(int port) {
                     server.receive(packet);
                     messagesReceived.add(
                         new String(packet.getData(), StandardCharsets.UTF_8).trim() + "\n");
-                    Thread.sleep(50);
+                    // The sleep duration here is shorter than that used in waitForMessage() at
+                    // 50ms.
+                    // Otherwise sometimes some messages seem to be lost, leading to flaky tests.
+                    Thread.sleep(15L);
                   }
 
                 } catch (Exception e) {