Fix broken test in SegmentReplicationSourceServiceTests.

Signed-off-by: Marc Handalian <handalm@amazon.com>

server/src/test/java/org/opensearch/indices/replication/SegmentReplicationSourceServiceTests.java

@@ -48,6 +48,7 @@ public void setUp() throws Exception {
         super.setUp();
         // setup mocks
         IndexShard mockIndexShard = CopyStateTests.createMockIndexShard();
+        when(mockIndexShard.verifyPrimaryMode()).thenReturn(true);
         ShardId testShardId = mockIndexShard.shardId();
         IndicesService mockIndicesService = mock(IndicesService.class);
         IndexService mockIndexService = mock(IndexService.class);