Regression with hash constraint seq postfix

[nojaf]

When generating a signature file the result is somewhat unexpected.

Repro steps

module Telplin

open System
open System.Threading.Tasks

let mapWithAdditionalDependenies
    (mapping: 'a -> 'b * #seq<#IDisposable>) 
    (value: Task<'a>) : Task<'b> =
    failwith "meh"

leads to

module Telplin

val mapWithAdditionalDependenies:
  mapping: ('a -> 'b * #'b1 seq) -> value: System.Threading.Tasks.Task<'a> -> System.Threading.Tasks.Task<'b>
    when 'b1 :> System.IDisposable

Expected behaviour

#'b1 seq used to be #seq<'b1> and they are not equivalent.
It should be #('b1 seq)

Actual behaviour

(5, 23) (5,27) warning 64
This construct causes code to be less generic than indicated by its type annotations. The type variable implied by the use of a '#', '_' or other type annotation at or near 'f940e587b40f4e3b887999b1d37cd776.fsi(5,23)-(5,27)' has been constrained to be type ''b1'.

Related information

This is due to the changes in #15280.
I'll try and fix this.

FCS: FSharpCheckFileResults.GenerateSignature