Make test more robust

Pick a less common name for the missing identifier. Depending
on my classpath I sometimes got `x is not a package` as an additional
error for this one.

Author: odersky

tests/neg/i1605.scala

@@ -1,5 +1,5 @@
 object Test {
   def foo = inlineMe
 
-  inline def inlineMe = 1 + x // error
+  inline def inlineMe = 1 + x2233 // error
 }