Update dependency com.diffplug.spotless:spotless-maven-plugin to v3.4.0

Author: renovate[bot]

parent_toplevel/pom.xml

@@ -235,7 +235,7 @@
       <plugin>
         <groupId>com.diffplug.spotless</groupId>
         <artifactId>spotless-maven-plugin</artifactId>
-        <version>3.3.0</version>
+        <version>3.4.0</version>
         <configuration>
           <java>
             <eclipse>