http.cookiejar.http2time raises ValueError instead of returning None for a strict-format fake month

Bug description

http.cookiejar.http2time() documents that it returns None for an
unrecognized date format, but its STRICT_DATE_RE fast path raises a raw
ValueError when the month field matches the pattern [JFMASOND][a-z][a-z]
yet names a month that does not exist:

>>> from http.cookiejar import http2time
>>> http2time('Wed, 09 Foo 1994 22:23:32 GMT')
Traceback (most recent call last):
  ...
ValueError: 'foo' is not in list
>>> http2time('Wed, 09 Feb 1994 22:23:32 GMT')   # a real month still works
760832612.0

The slower parser (_str2time) already handles the same input via
try/except and returns None; only the strict fast path leaks. It is
reachable from parse_ns_headers() through a cookie's expires= attribute,
e.g. Set-Cookie: x=y; expires=Wed, 09 Foo 1994 22:23:32 GMT.

gh-60385 previously established the "returns None, never raises" contract
for a different http2time code path; the later STRICT_DATE_RE fast path
reintroduced a leak on this separate path.

CPython versions tested on

3.13, 3.14, 3.15

Operating systems tested on

Linux, macOS

Linked PRs

• gh-153678

Comienza en el módulo http.cookiejar de Python siguiendo http2time() a través de la ruta rápida STRICT_DATE_RE y comparándolo con el tratamiento que hace _str2time de los meses no válidos. El cambio estará terminado cuando un mes falso con formato estricto devuelva None sin lanzar una excepción, mientras que un mes válido siga analizándose correctamente; considera la ruta de expiración de cookies de parse_ns_headers() descrita en el issue.