Issue #375: update to checkstyle 9.0.1

Author: muhlba91

README.md

@@ -21,6 +21,7 @@ Compatibility matrix from checkstyle team:
 
 Checkstyle Plugin|Sonar min|Sonar max|Checkstyle|Jdk
 -----------------|---------|---------|----------|---
+9.0.1|8.9  |8.9+|9.0.1|1.8
 8.45.1|7.9  |7.9+|8.45.1|1.8
 8.42|7.9  |7.9+|8.42|1.8
 8.41.1|7.9  |7.9+|8.41.1|1.8

pom.xml

@@ -93,7 +93,7 @@
   </ciManagement>
 
   <properties>
-    <checkstyle.version>8.45.1</checkstyle.version>
+    <checkstyle.version>9.0.1</checkstyle.version>
     <sonar.version>8.9.3.48735</sonar.version>
     <sonar-java.version>7.2.0.26923</sonar-java.version>
     <maven.checkstyle.plugin.version>3.1.2</maven.checkstyle.plugin.version>