Maven pom.xml(deps-dev): Bump xmlunit.version from 2.6.4 to 2.9.0

Bumps `xmlunit.version` from 2.6.4 to 2.9.0.

Updates `xmlunit-core` from 2.6.4 to 2.9.0
- [Release notes](https://github.com/xmlunit/xmlunit/releases)
- [Changelog](https://github.com/xmlunit/xmlunit/blob/main/RELEASE_NOTES.md)
- [Commits](xmlunit/xmlunit@v2.6.4...v2.9.0)

Updates `xmlunit-matchers` from 2.6.4 to 2.9.0
- [Release notes](https://github.com/xmlunit/xmlunit/releases)
- [Changelog](https://github.com/xmlunit/xmlunit/blob/main/RELEASE_NOTES.md)
- [Commits](xmlunit/xmlunit@v2.6.4...v2.9.0)

---
updated-dependencies:
- dependency-name: org.xmlunit:xmlunit-core
  dependency-type: direct:development
  update-type: version-update:semver-minor
- dependency-name: org.xmlunit:xmlunit-matchers
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

pom.xml

@@ -42,7 +42,7 @@
 
         <lombok.version>1.18.22</lombok.version>
         <quarkus.version>2.7.5.Final</quarkus.version>
-        <xmlunit.version>2.6.4</xmlunit.version>
+        <xmlunit.version>2.9.0</xmlunit.version>
     </properties>
 
     <url>https://project-openubl.github.io/</url>