fix: update Checkstyle and Maven Resources Plugin versions; remove obsolete sync-merge-upstream.sh script

Author: brunoborges

pom.xml

@@ -194,15 +194,15 @@
                     <dependency>
                         <groupId>com.puppycrawl.tools</groupId>
                         <artifactId>checkstyle</artifactId>
-                        <version>10.21.4</version>
+                        <version>10.26.1</version>
                     </dependency>
                 </dependencies>
             </plugin>
             <!-- Filter site markdown files to replace ${project.version} -->
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-resources-plugin</artifactId>
-                <version>3.3.1</version>
+                <version>3.4.0</version>
                 <executions>
                     <execution>
                         <id>filter-site-markdown</id>