Update spotless-maven-plugin to 2.43.0 for Java 21 compatibility

The previous spotless version has Java 21 compatibility issues,
see diffplug/spotless#1791 for more.

Author: fourls

server/pom.xml

@@ -100,7 +100,7 @@
         <plugin>
           <groupId>com.diffplug.spotless</groupId>
           <artifactId>spotless-maven-plugin</artifactId>
-          <version>2.27.2</version>
+          <version>2.43.0</version>
           <configuration>
             <java>
               <googleJavaFormat>