Fix a flaky test that forces materialization to hit cache

Signed-off-by: Joe Liu <[email protected]>

Author: liuguoqingfz

server/src/test/java/org/opensearch/index/fielddata/IndexFieldDataServiceTests.java

@@ -185,6 +185,10 @@ public void onRemoval(ShardId shardId, String fieldName, boolean wasEvicted, lon
         LeafFieldData loadField1 = ifd1.load(leafReaderContext);
         LeafFieldData loadField2 = ifd2.load(leafReaderContext);
 
+        // Force materialization so both hit the shared cache
+        loadField1.getBytesValues();
+        loadField2.getBytesValues();
+
         assertEquals(2, indicesService.getIndicesFieldDataCache().getCache().count());
 
         // Remove index