LSP causes configuration caching to fail

[Phoenix-Starlight]

At line 56 of https://github.com/fwcd/kotlin-language-server/blob/main/shared/src/main/resources/projectClassPathFinder.gradle
inside the doLast block, it references a SourceSet which is not permitted.

Currently this is causing configuration caching problems.

[fwcd]

A PR would be very welcome