Assume release compiler

Author: odersky

compiler/src/dotty/tools/dotc/config/Config.scala

@@ -219,7 +219,7 @@ object Config {
   /** Turn on in order to test the CI assuming we have a stable release compiler
    *  instead of a nightly or snapshot.
    */
-  private val assumeNonExperimentalCompiler = false
+  private val assumeNonExperimentalCompiler = true
 
   /** Are experimental features are allowed? By default same as
    *  `Properties.experimental`. Can be re-assigned, e.g. to allow tests