Modified singletonWitnessAs to use valueOf instead of constValue for Scala 3

[mpskowron]

This doesn't compile for Scala 3.0.1

import eu.timepit.refined.generic.Equal
import eu.timepit.refined.collection.Size
import eu.timepit.refined.refineV

val size = 2

val arr = refineV[Size[Equal[size.type]]](Array(1, 2))

Error message:

  |val arr = refineV[Size[Equal[size.type]]](Array(1, 2))
  |                                                      ^
  |                 not a constant type: (size : Int); cannot take constValue
  | This location contains code that was inlined from WitnessAs.scala:39

However, this does compile:

import eu.timepit.refined.generic.Equal
import eu.timepit.refined.collection.Size
import eu.timepit.refined.refineV
import eu.timepit.refined.internal.WitnessAs

inline given singletonWitnessAs[B, A <: B: ValueOf]: WitnessAs[A, B] = {
  val a = valueOf[A]
  WitnessAs(a, a)
}
val size = 2
val arr = refineV[Size[Equal[size.type]]](Array(1, 2))

Using refined with modified "signletonWitnessAs" also compiles. I don't know if this is correct fix for the issue, hope it is.

[codecov]

Codecov Report

Merging #998 (f76973a) into master (01c5220) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #998   +/-   ##
=======================================
  Coverage   92.39%   92.39%           
=======================================
  Files          63       63           
  Lines         815      815           
  Branches        6        6           
=======================================
  Hits          753      753           
  Misses         62       62           

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