Put source version 2.13 in its proper place

It should come before 3.0

Author: odersky

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

@@ -8,6 +8,8 @@ import Feature.isPreviewEnabled
 import util.Property
 
 enum SourceVersion:
+  case `2.13`
+
   case `3.0-migration`, `3.0`
   case `3.1-migration`, `3.1`
   case `3.2-migration`, `3.2`
@@ -20,7 +22,6 @@ enum SourceVersion:
   case `3.9-migration`, `3.9`
   // Add 3.x-migration and 3.x here
   // !!! Keep in sync with scala.runtime.stdlibPatches.language !!!
-  case `2.13`
   case `future-migration`, `future`
 
   case `never`    // needed for MigrationVersion.errorFrom if we never want to issue an error