Remove default dependencies from a test suite when test folder does not exist

[jjohannes]

When you like to fully control versions yourself, you can configure test suites with useJUnitJupiter("") (no version).
When combining this plugin with java-module-dependencies this is often the desired setup.

However, this can lead to failing builds, if a test suite is setup (e.g. test, which always exists) but is not used. This is because dependency resolution might be done before the task is recognized as NO-SOURCE.

To prevent this, the default test dependencies should be removed if the source folders of a test suite do not exist.