Fixes invalid exclusion paths

[rpau]

What's changed?

The exclusion paths were calculated from the parent project path instead of the base dir. This has caused duplicated source files in the Moderne Gradle plugin.

What's your motivation?

Duplicated source files in the LSTs we generate.

Anything in particular you'd like reviewers to focus on?

• I required to add the rewrite dependencies as a testRuntime dependencies to properly add a test that was failing before and now succeeds.

Anyone you would like to review specifically?

@knutwannheden @sambsnyd @jkschneider

[rpau]

To have a green build, we need to merge https://github.com/openrewrite/rewrite-gradle-plugin/pull/214 first because the main branch is broken