Upgrade Checkstyle 10.2 -> 10.12.6

See:
- https://checkstyle.sourceforge.io/releasenotes.html

pom.xml

@@ -435,7 +435,7 @@
                         <dependency>
                             <groupId>com.puppycrawl.tools</groupId>
                             <artifactId>checkstyle</artifactId>
-                            <version>10.2</version>
+                            <version>10.12.6</version>
                         </dependency>
                     </dependencies>
                     <executions>