Update dependency org.xmlunit:xmlunit-assertj3 to v2.9.1

Author: renovate[bot]

pom.xml

@@ -26,7 +26,7 @@
     <commons.lang.version>3.12.0</commons.lang.version>
     <commons.commons-exec>1.3</commons.commons-exec>
     <xml-unit-core.version>2.8.4</xml-unit-core.version>
-    <xml-unit-assertj.version>2.8.4</xml-unit-assertj.version>
+    <xml-unit-assertj.version>2.9.1</xml-unit-assertj.version>
   </properties>
 
   <scm>