When the XMLUnit2 upgrade was done (commit: c39d3d1) this import was forgotten.
It causes the bug reported with XMLUnit1 (issue: #1193) to still be present when using `ResultMatchers#soapEnvelope(Source)`.
For more infos: https://github.com/spring-projects/spring-ws/issues/1193#issuecomment-1650162836
See #1370.
Related: #1193.