Fix compile-time warnings (excluding Javadoc-related ones)

Author: backpaper0

pom.xml

@@ -187,6 +187,20 @@
                 </configuration>
             </plugin>
         </plugins>
+        <pluginManagement>
+            <plugins>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-compiler-plugin</artifactId>
+                    <version>3.13.0</version>
+                </plugin>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-jar-plugin</artifactId>
+                    <version>3.4.1</version>
+                </plugin>
+            </plugins>
+        </pluginManagement>
     </build>
 
     <repositories>