update to jdk 21

pdb-js/build.gradle

@@ -3,6 +3,7 @@ import java.nio.file.Paths
 
 plugins {
 	id("com.github.node-gradle.node") version "7.0.0"
+	id("java-library") // not sure why this is needed - is already set in /build.gradle - but without it the project sometimes (not always) is not configured as a java project
 }