MQE-741: two steps with same step key, the later step will overwrite the previous step.

 - improve performance

Author: okolesnyk

src/Magento/FunctionalTestingFramework/Test/etc/mergedTestSchema.xsd

@@ -53,6 +53,7 @@
         </xs:choice>
         <xs:attribute type="xs:string" name="name"/>
         <xs:attribute type="xs:boolean" name="remove" default="false"/>
+        <xs:attribute type="xs:string" name="filename" />
     </xs:complexType>
     <xs:group name="testTypeTags">
         <xs:choice>