Fix warnings in compiler code and tests

compiler/tests-mutes/build.gradle.kts

@@ -17,9 +17,12 @@ sourceSets {
     "test" {}
 }
 
+val compileKotlin: org.jetbrains.kotlin.gradle.tasks.KotlinCompile by tasks
+compileKotlin.kotlinOptions.freeCompilerArgs += "-Xskip-runtime-version-check"
+
 val mutesPackageName = "org.jetbrains.kotlin.test.mutes"
 
 application {
     mainClassName = "$mutesPackageName.MutedTestsSyncKt"
     applicationDefaultJvmArgs = rootProject.properties.filterKeys { it.startsWith(mutesPackageName) }.map { (k, v) -> "-D$k=$v" }
-}
+}