incorrect "http.cookiejar bug" when catching exception

Bug report

catching certain exceptions from the http.cookiejar module incorrectly triggers an "unhandled exception" warning:

#!/usr/bin/env python3

import logging
from http.cookiejar import LoadError, MozillaCookieJar
from tempfile import NamedTemporaryFile

logging.basicConfig()
log = logging.getLogger()

with NamedTemporaryFile(mode="w") as tmp:
    tmp.write("# Netscape HTTP Cookie File\n%3D\n")
    tmp.seek(0)
    jar = MozillaCookieJar(tmp.name)

    try:
        jar.load()
    except LoadError:
        log.warning("Failed to load cookies")

alexia@cadoth ~ > ./http_cookiejar_bug.py  
/home/alexia/.local/share/pyenv/versions/3.11.0/lib/python3.11/http/cookiejar.py:2080: UserWarning: http.cookiejar bug!
Traceback (most recent call last):
  File "/home/alexia/.local/share/pyenv/versions/3.11.0/lib/python3.11/http/cookiejar.py", line 2041, in _really_load
    domain, domain_specified, path, secure, expires, name, value = \
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: not enough values to unpack (expected 7, got 1)

  _warn_unhandled_exception()
WARNING:root:Failed to load cookies

Your environment

• CPython versions tested on: 3.9.2, 3.10.8, 3.11.0
• Operating system and architecture: Debian 11 amd64

Linked PRs

• gh-99676
• gh-139395

从 Lib/http/cookiejar.py 中的 _really_load 和 _warn_unhandled_exception 开始，使用 issue 中的 reproducer 观察捕获 LoadError 时的警告。检查相关的 PR gh-99676 和 gh-139395，然后添加或更新一个回归测试，证明这个已处理的格式错误 cookie 情况不再产生错误警告。