Enable --warn-redundant-casts option in mypy (#14671)

* Enable `--warn-redundant-casts` option in mypy

Doesn't do much but helps me sleep better at night.

* Changelog

* Fix name of the ignore

* Fix one more missed cast

Not sure why I didn't see this one locally, maybe I needed a poetry update

* Remove old comment

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

scripts-dev/release.py

@@ -27,7 +27,7 @@ import time
 import urllib.request
 from os import path
 from tempfile import TemporaryDirectory
-from typing import Any, List, Optional, cast
+from typing import Any, List, Optional
 
 import attr
 import click
@@ -174,9 +174,7 @@ def _prepare() -> None:
         click.get_current_context().abort()
 
     # Switch to the release branch.
-    # Cast safety: parse() won't return a version.LegacyVersion from our
-    # version string format.
-    parsed_new_version = cast(version.Version, version.parse(new_version))
+    parsed_new_version = version.parse(new_version)
 
     # We assume for debian changelogs that we only do RCs or full releases.
     assert not parsed_new_version.is_devrelease