Update xmlunit.version to v2.9.0 (#2474)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

core/pom.xml

@@ -17,7 +17,7 @@
         <jackson-databind.version>2.13.1</jackson-databind.version>
         <jsoup.version>1.14.3</jsoup.version>
         <junit-jupiter.version>5.8.2</junit-jupiter.version>
-        <xmlunit.version>2.8.4</xmlunit.version>
+        <xmlunit.version>2.9.0</xmlunit.version>
         <hamcrest.version>2.2</hamcrest.version>
         <hamcrest-json.version>0.2</hamcrest-json.version>
         <mockito.version>4.3.0</mockito.version>