unused local definition warning when defining focus inside a function

case class Lecturer(firstName: String, lastName: String, salary: Int)
case class Department(budget: Int, lecturers: List[Lecturer])
case class University(name: String, departments: Map[String, Department])

val uni = University("oxford", Map(
  "Computer Science" -> Department(45, List(
    Lecturer("john"  , "doe", 10),
    Lecturer("robert", "johnson", 16)
  )),
  "History" -> Department(30, List(
    Lecturer("arnold", "stones", 20)
  ))
))

import monocle.Focus
import monocle.syntax.all._

val departmentsWorks = Focus[University](_.departments)
departmentsWorks.at("History").replace(None)(uni)

def foo() = {

  //warning unused local definition
  val departments = Focus[University](_.departments)
  departments.at("History").replace(None)(uni)
}

foo()

Scastie: https://scastie.scala-lang.org/TfVaZDtKSmKGrgQuI7N3Rg

versions:
scala 3.5.2
monocle 3.3.0

Start with the Scastie reproducer and compare the top-level FocusUniversity definition with the same definition inside foo(). Check how the local definition is expanded or inferred in Scala 3. Done means the valid local use no longer produces an unused local definition warning, while the existing optic behavior remains unchanged.