Upgrade TestNG 7.8.0 -> 7.9.0 (#942)

See:
- https://github.com/testng-team/testng/releases/tag/7.9.0
- testng-team/testng@7.8.0...7.9.0

pom.xml

@@ -473,7 +473,7 @@
             <dependency>
                 <groupId>org.testng</groupId>
                 <artifactId>testng</artifactId>
-                <version>7.8.0</version>
+                <version>7.9.0</version>
             </dependency>
         </dependencies>
     </dependencyManagement>