escape error message in test

[Cherry-picked bcdf5e7]

Author: bishabosha

tests/run-with-compiler/i14541.scala

@@ -6,6 +6,7 @@ object Test:
   def main(args: Array[String]): Unit =
     getClass.getClassLoader.run("echo", List("hello", "raw", "world"))
     // caution: uses "SCALA_OPTS"
+    sys.props("scala.use_legacy_launcher") = "true"
     dotty.tools.MainGenericRunner.main(Array("--class-path", classpath, "echo", "hello", "run", "world"))
 
 @main def echo(args: String*): Unit = println {