Use client_error instead of a hard-coded exception in TCPConnector

`client_error` is an existing method argument. And it seems that it is supposed to be used in the two places instead of the hard-coded exception.

CHANGES/5502.bugfix

@@ -0,0 +1,2 @@
+Use variable ``client_error`` instead of a hard-coded ``ClientConnectorError`` exception
+in ``TCPConnector``.

aiohttp/connector.py

@@ -985,7 +985,7 @@ def drop_exception(fut: "asyncio.Future[List[Dict[str, Any]]]") -> None:
         except OSError as exc:
             # in case of proxy it is not ClientProxyConnectionError
             # it is problem of resolving proxy ip itself
-            raise ClientConnectorError(req.connection_key, exc) from exc
+            raise client_error(req.connection_key, exc) from exc
 
         last_exc = None  # type: Optional[Exception]
 
@@ -1008,7 +1008,7 @@ def drop_exception(fut: "asyncio.Future[List[Dict[str, Any]]]") -> None:
                     req=req,
                     client_error=client_error,
                 )
-            except ClientConnectorError as exc:
+            except client_error as exc:
                 last_exc = exc
                 continue