Use Maven profiles to handle different versions of TestNG

For JDK8, bump org.testng:testng to the last supported release for
this version i.e. 7.5
For JDK11+, bump org.testng:testng to the latest release 7.9.0

pom.xml

@@ -192,13 +192,6 @@
       <version>2.7.3</version>
       <scope>runtime</scope>
     </dependency>
-
-    <dependency>
-      <groupId>org.testng</groupId>
-      <artifactId>testng</artifactId>
-      <version>6.8</version>
-      <scope>test</scope>
-    </dependency>
   </dependencies>
 
   <properties>
@@ -472,5 +465,33 @@
         </plugins>
       </build>
     </profile>
+    <profile>
+      <id>jdk8-only</id>
+      <activation>
+        <jdk>(,11)</jdk>
+      </activation>
+      <dependencies>
+        <dependency>
+          <groupId>org.testng</groupId>
+          <artifactId>testng</artifactId>
+          <version>7.5</version>
+          <scope>test</scope>
+        </dependency>
+      </dependencies>
+    </profile>
+    <profile>
+      <id>jdk11+</id>
+      <activation>
+        <jdk>[11,)</jdk>
+      </activation>
+      <dependencies>
+        <dependency>
+          <groupId>org.testng</groupId>
+          <artifactId>testng</artifactId>
+          <version>7.9.0</version>
+          <scope>test</scope>
+        </dependency>
+      </dependencies>
+    </profile>
   </profiles>
 </project>