Downgrade to Checkstyle 8.x as 9.x series has much larger memory usage

By: md_5 <git@md-5.net>

paper-server/pom.xml

@@ -447,7 +447,7 @@
                             <dependency>
                                 <groupId>com.puppycrawl.tools</groupId>
                                 <artifactId>checkstyle</artifactId>
-                                <version>9.1</version>
+                                <version>8.45.1</version>
                             </dependency>
                         </dependencies>
                     </plugin>