chore(deps): bump com.helger.maven:ph-schematron-maven-plugin

Bumps [com.helger.maven:ph-schematron-maven-plugin](https://github.com/phax/ph-schematron) from 6.3.3 to 9.1.0.
- [Release notes](https://github.com/phax/ph-schematron/releases)
- [Commits](phax/ph-schematron@ph-schematron-parent-pom-6.3.3...ph-schematron-parent-pom-9.1.0)

---
updated-dependencies:
- dependency-name: com.helger.maven:ph-schematron-maven-plugin
  dependency-version: 9.1.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

pom.xml

@@ -236,7 +236,7 @@
       <plugin>
         <groupId>com.helger.maven</groupId>
         <artifactId>ph-schematron-maven-plugin</artifactId>
-        <version>6.3.3</version>
+        <version>9.1.0</version>
         <executions>
           <execution>
             <goals>