testwwvb: better(?) alternative

avoids typing.cast & pyrefly: ignore

test/testwwvb.py

@@ -14,7 +14,6 @@ import io
 import pathlib
 import random
 import sys
-import typing
 import unittest
 
 import uwwvb
@@ -48,13 +47,12 @@ class WWVBTestCase(unittest.TestCase):
                 channel: WWVBChannel = "amplitude"
                 style = "default"
                 for o in options:
-                    if o.startswith("--channel="):
-                        value = o[10:]
-                        if value in {"both", "amplitude", "phase"}:
-                            # pyrefly: ignore  # redundant-cast
-                            channel = typing.cast("WWVBChannel", value)
-                        else:
-                            raise ValueError(f"Unknown channel {o!r}")
+                    if o == "--channel=both":
+                        channel = "both"
+                    elif o == "--channel=amplitude":
+                        channel = "amplitude"
+                    elif o == "--channel=phase":
+                        channel = "phase"
                     elif o.startswith("--style="):
                         style = o[8:]
                     else: