Temporary disable TestNg if user's JDK is less that 11

[EgorkaKulikov]

Description

TestNg beginning from 7.6.0 requires minimal JDK dependency version to be 11.
https://groups.google.com/g/testng-users/c/BAFB1vk-kok

Expected behavior

If user's JDK version is less than 11, we should install version 7.5 of TestNg
Unfortunately, it is impossible now because of a bug in gradle-intellij-plugin version 2020.2
So current solution is to prohibit using TestNg in projects with JDK version less than 11.