Use static year range in copyright of generated FIR and tests

Dynamically calculating a year is problematic, especially in cases like
FIR where generation happens in every build. When you are working on a
last year's commit, each build creates a bunch of uncommited
 changes of updating the year in copyrights.

compiler/fir/tree/build.gradle.kts

@@ -40,6 +40,7 @@ val generateTree by tasks.registering(NoDebugJavaExec::class) {
     outputs.dirs(generationRoot)
 
     args(generationRoot)
+    workingDir = rootDir
     classpath = generatorClasspath
     main = "org.jetbrains.kotlin.fir.tree.generator.MainKt"
     systemProperties["line.separator"] = "\n"