Bump com.puppycrawl.tools:checkstyle from 10.20.2 to 10.21.0 (#951)

Author: dependabot[bot]

pom.xml

@@ -191,7 +191,7 @@
             <dependency>
               <groupId>com.puppycrawl.tools</groupId>
               <artifactId>checkstyle</artifactId>
-              <version>10.20.2</version>
+              <version>10.21.0</version>
             </dependency>
           </dependencies>
         </plugin>