Move test to avoid pickling issues

Author: odersky

tests/pos-custom-args/captures/i18699.scala

@@ -0,0 +1,7 @@
+import language.experimental.captureChecking
+trait Cap:
+  def use: Int = 42
+
+def test2(cs: List[Cap^]): Unit =
+  val t0: Cap^{cap[test2]} = cs.head  // error
+  var t1: Cap^{cap[test2]} = cs.head  // error