non_constant_identifier_names: New Function syntax

[matanlurey]

This (Function below) is linted, but it shouldn't be, ifAbsent the identifier name:

  // ignore: non_constant_identifier_names
  Future<T> writeIfAbsent<T>(String key, T Function<T> ifAbsent) {
    // TODO: implement writeIfAbsent
  }

[matanlurey]

Oops, turns out this is another bug, not an issue with the linter:

#30760