[1448] Exclude referenced libraries from validation

[gdaniel]

Fixes #1448

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[gdaniel]

I moved this away from the @BeforeEach because I needed to check stuff before the import.
In any case, I think this class should be reworked because it doesn't rely on the GraphQL APIs like the other integration tests (see for example line 207 projectEditingContextEventProcessor.handle which hooks into the event processor instead of a query runner).

This is not the scope of this PR though, so I adapted the code to fit my new test case.