[NI] Relax requirement for stub types in builder-inference

For functions with implicit return type annotations will be replaced
 anyway in order to initialize return type, so this restriction in
 `StubType` was too strong

 #KT-30656 Fixed

core/descriptors/src/org/jetbrains/kotlin/types/StubType.kt

@@ -24,9 +24,7 @@ class StubType(
     override val annotations: Annotations
         get() = Annotations.EMPTY
 
-    override fun replaceAnnotations(newAnnotations: Annotations): SimpleType {
-        error("Shouldn't be called on non-fixed type")
-    }
+    override fun replaceAnnotations(newAnnotations: Annotations): SimpleType = this
 
     override fun makeNullableAsSpecified(newNullability: Boolean): SimpleType {
         return if (newNullability == isMarkedNullable)