minor: Use literal list syntax instead of a descending range

This removes a warning from `4..1` present in Elixir 1.17+. We don't
switch to `4..1//-1` so that we can maintain compatibility with Elixir
versions before the range-step syntax was introduced.

Author: the-mikedavis

CHANGELOG.md

@@ -6,6 +6,13 @@ The format is based on [Keep a
 Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to
 [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed
+
+- Fixed a compilation warning present with Elixir 1.17+ about "`4..1`" not
+  using a range step.
+
 ## 1.0.3 - 2023-04-16
 
 ### Fixed

lib/mint/web_socket/frame.ex

@@ -183,7 +183,10 @@ defmodule Mint.WebSocket.Frame do
   # n=4 is the happy path
   # n=3..1 catches cases where the remaining byte_size/1 of the payload is shorter
   # than the mask
-  for n <- 4..1 do
+  # MINOR: We use a literal list instead of `4..1` to avoid compilation warnings on
+  # Elixir 1.17+ and instead of `4..1//-1` to maintain compatibility with older
+  # Elixir versions that do not support the range-step syntax.
+  for n <- [4, 3, 2, 1] do
     def apply_mask(
           <<part_key::integer-size(8)-unit(unquote(n)), payload_rest::binary>>,
           <<mask_key::integer-size(8)-unit(unquote(n)), _::binary>> = mask,