Stop using the cgi module, deprecated in Python 3.11 per PEP 594 (aio…

…-libs#6708)

* Stop using the cgi module, deprecated in Python 3.11 per PEP 594

https://peps.python.org/pep-0594/#cgi

* Simplify creating params dict

Co-authored-by: Sam Bull <aa6bs0@sambull.org>

* Create 6708.misc

Co-authored-by: Sam Bull <aa6bs0@sambull.org>
(cherry picked from commit a045480)

CHANGES/6708.misc

@@ -0,0 +1 @@
+Replace deprecated cgi module usage with email.parser.

aiohttp/helpers.py

@@ -3,7 +3,6 @@
 import asyncio
 import base64
 import binascii
-import cgi
 import datetime
 import enum
 import functools
@@ -18,6 +17,7 @@
 import weakref
 from collections import namedtuple
 from contextlib import suppress
+from email.parser import HeaderParser
 from email.utils import parsedate
 from math import ceil
 from pathlib import Path
@@ -768,7 +768,10 @@ def _parse_content_type(self, raw: Optional[str]) -> None:
             self._content_type = "application/octet-stream"
             self._content_dict = {}
         else:
-            self._content_type, self._content_dict = cgi.parse_header(raw)
+            msg = HeaderParser().parsestr("Content-Type: " + raw)
+            self._content_type = msg.get_content_type()
+            params = msg.get_params()
+            self._content_dict = dict(params[1:])  # First element is content type again
 
     @property
     def content_type(self) -> str: