Re-enable keep-alive on proxies (#8920)

(cherry picked from commit 5cf5db5)

Author: Dreamsorcerer

CHANGES/8920.misc.rst

@@ -0,0 +1 @@
+Enabled keep-alive support on proxies (which was originally disabled several years ago) -- by :user:`Dreamsorcerer`.

aiohttp/client_proto.py

@@ -62,9 +62,6 @@ def should_close(self) -> bool:
             or bool(self._tail)
         )
 
-    def force_close(self) -> None:
-        self._should_close = True
-
     def close(self) -> None:
         transport = self.transport
         if transport is not None:

aiohttp/connector.py

@@ -1376,11 +1376,6 @@ async def _create_proxy_connection(
             proxy_req, [], timeout, client_error=ClientProxyConnectionError
         )
 
-        # Many HTTP proxies has buggy keepalive support.  Let's not
-        # reuse connection but close it after processing every
-        # response.
-        proto.force_close()
-
         auth = proxy_req.headers.pop(hdrs.AUTHORIZATION, None)
         if auth is not None:
             if not req.is_ssl():