Incorrect default test root on antlr project

[EgorkaKulikov]

To Reproduce

• Download antlr project from Git (https://github.com/antlr/antlr4)
• Find method setGrammarPtr
• Try to create tests for it with UtBot Intellij Plugin
• Default test root is selected incorrectly, after we click OK an error message appears

The error is that test source root is located out of content entry.

Visual proofs (screenshots, logs, images)