Groovy compiler generates invalid Java stubs

> Task :test-kit:compileIntegTestGroovy FAILED
Executing Spock 2.0.0-groovy-3.0 with NOT compatible Groovy version 4.0.0-beta-1 due to set spock.iKnowWhatImDoing.disableGroovyVersionCheck system property. This is unsupported and may result in weird runtime errors!
/Users/lptr/Workspace/gradle/gradle/subprojects/test-kit/build/tmp/compileIntegTestGroovy/groovy-java-stubs/org/gradle/testkit/runner/BaseGradleRunnerIntegrationTest.java:92: error: '.class' expected
protected final boolean debug = new java.lang.Boolean((boolean -> boolean)false);
                                                               ^
/Users/lptr/Workspace/gradle/gradle/subprojects/test-kit/build/tmp/compileIntegTestGroovy/groovy-java-stubs/org/gradle/testkit/runner/BaseGradleRunnerIntegrationTest.java:92: error: <identifier> expected
protected final boolean debug = new java.lang.Boolean((boolean -> boolean)false);
                                                                         ^
/Users/lptr/Workspace/gradle/gradle/subprojects/test-kit/build/tmp/compileIntegTestGroovy/groovy-java-stubs/org/gradle/testkit/runner/BaseGradleRunnerIntegrationTest.java:92: error: unexpected type
protected final boolean debug = new java.lang.Boolean((boolean -> boolean)false);
                                                       ^
  required: value
  found:    class
3 errors
startup failed:
Compilation failed; see the compiler error output for details.

1 error