build(deps): bump xmlunit.version from 2.9.0 to 2.9.1

Bumps `xmlunit.version` from 2.9.0 to 2.9.1.

Updates `xmlunit-core` from 2.9.0 to 2.9.1
- [Release notes](https://github.com/xmlunit/xmlunit/releases)
- [Changelog](https://github.com/xmlunit/xmlunit/blob/main/RELEASE_NOTES.md)
- [Commits](xmlunit/xmlunit@v2.9.0...v2.9.1)

Updates `xmlunit-matchers` from 2.9.0 to 2.9.1
- [Release notes](https://github.com/xmlunit/xmlunit/releases)
- [Changelog](https://github.com/xmlunit/xmlunit/blob/main/RELEASE_NOTES.md)
- [Commits](xmlunit/xmlunit@v2.9.0...v2.9.1)

Updates `xmlunit-legacy` from 2.9.0 to 2.9.1
- [Release notes](https://github.com/xmlunit/xmlunit/releases)
- [Changelog](https://github.com/xmlunit/xmlunit/blob/main/RELEASE_NOTES.md)
- [Commits](xmlunit/xmlunit@v2.9.0...v2.9.1)

---
updated-dependencies:
- dependency-name: org.xmlunit:xmlunit-core
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.xmlunit:xmlunit-matchers
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.xmlunit:xmlunit-legacy
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

exist-parent/pom.xml

@@ -118,7 +118,7 @@
         <milton.version>1.8.1.3</milton.version>
         <saxon.version>9.9.1-8</saxon.version>
         <xmlresolver.version>4.6.0</xmlresolver.version>
-        <xmlunit.version>2.9.0</xmlunit.version>
+        <xmlunit.version>2.9.1</xmlunit.version>
         <junit.version>4.13.2</junit.version>
         <junit.jupiter.version>5.9.1</junit.jupiter.version>
         <junit.vintage.version>5.9.2</junit.vintage.version>