IndexEventHandlerTest: Fix 'Unlikely argument type' Eclipse warnings

Eclipse 4.7.0 (Oxygen) introduced a new compiler warning:

  Unlikely argument type

In this case the warning is being emitted because a String is being
passed in place of Index{Account|Change|Group}Task instance.

Replace these with dummy instances of the expected class.

Change-Id: I2c44501c4e0da63f88ad22d1a4a91ff55bed025c
diff --git a/src/test/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandlerTest.java b/src/test/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandlerTest.java
index e50d713..60c5ab7 100644
--- a/src/test/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandlerTest.java
+++ b/src/test/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandlerTest.java
@@ -143,7 +143,7 @@
     assertThat(task.hashCode()).isEqualTo(identicalTask.hashCode());
 
     assertThat(task.equals(null)).isFalse();
-    assertThat(task.equals("test")).isFalse();
+    assertThat(task.equals(indexEventHandler.new IndexChangeTask(CHANGE_ID + 1, false))).isFalse();
     assertThat(task.hashCode()).isNotEqualTo("test".hashCode());
 
     IndexChangeTask differentChangeIdTask = indexEventHandler.new IndexChangeTask(123, false);
@@ -167,7 +167,7 @@
     assertThat(task.hashCode()).isEqualTo(identicalTask.hashCode());
 
     assertThat(task.equals(null)).isFalse();
-    assertThat(task.equals("test")).isFalse();
+    assertThat(task.equals(indexEventHandler.new IndexAccountTask(ACCOUNT_ID + 1))).isFalse();
     assertThat(task.hashCode()).isNotEqualTo("test".hashCode());
 
     IndexAccountTask differentAccountIdTask = indexEventHandler.new IndexAccountTask(123);