Bump tasty format for 28.6.x (#21378)

[test_non_bootstrapped]

Fixes:
https://github.com/scala/scala3/actions/runs/10366706352/job/28696553741

Author: hamzaremmal

tasty/src/dotty/tools/tasty/TastyFormat.scala

@@ -324,7 +324,7 @@ object TastyFormat {
    *  compatibility, but remains backwards compatible, with all
    *  preceding `MinorVersion`.
    */
-  final val MinorVersion: Int = 5
+  final val MinorVersion: Int = 6
 
   /** Natural Number. The `ExperimentalVersion` allows for
    *  experimentation with changes to TASTy without committing