Add -no-warn to a Bytecode test

[OlivierBlanvillain]

This PR silences a warning in test, thus making tests output more uniform.

This test in question is expected to produce a warning, but it ends up in the CI output and looks like an error:

-- [E115] Syntax Warning:
object Foo {
  import scala.annotation.switch
  def foo(i: Any) = (i: @switch) match {
    case x: String => println("string!")
    case x :: xs   => println("list!")
  }
}:4:33
4 |  def foo(i: Any) = (i: @switch) match {
  |                    ^
  |Could not emit switch for @switch annotated match since there are not
enough cases
5 |    case x: String => println("string!")
6 |    case x :: xs   => println("list!")
7 |  }