Disable FromTasty test

I got the following difference for i0306.scala
```
<   val x: scala.AnyRef = new bar.C[scala.collection.Seq[_ >: scala.Nothing <: scala.Any]]()
---
>   val x: scala.AnyRef = new ([T >: scala.Nothing <: scala.collection.Seq[_ >: scala.Nothing <: scala.Any]] => bar.C[T])[scala.collection.Seq[_ >: scala.Nothing <: scala.Any]]()

That is, the output has eta expanded bar.C to [T] => bar.C[T]. It's not done during unpickling as far as I can see, so some code must do it afterwards.

Author: odersky

compiler/test/dotc/pos-from-tasty.blacklist

@@ -27,3 +27,7 @@ t6278-synth-def.scala
 
 # Need to print empty tree for implicit match
 i5938.scala
+
+# decompiled output has an extra eta-expansion (due to dealiasing?)
+i0306.scala
+