Upgrade to Maven Wrapper 3.9.1.

See #491

Author: mp911de

.mvn/wrapper/maven-wrapper.properties

@@ -1,2 +1,2 @@
-#Mon Feb 20 11:58:10 CET 2023
-distributionUrl=https\://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.0/apache-maven-3.9.0-bin.zip
+#Thu Apr 06 16:16:27 CEST 2023
+distributionUrl=https\://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.1/apache-maven-3.9.1-bin.zip