Fix aiohttp patch not working on newer versions

discord/http.py

@@ -325,8 +325,12 @@ class MaybeUnlock:
 # For some reason, the Discord voice websocket expects this header to be
 # completely lowercase while aiohttp respects spec and does it as case-insensitive
 aiohttp.hdrs.WEBSOCKET = 'websocket'  # type: ignore
-# Support brotli if installed
-aiohttp.client_reqrep.ClientRequest.DEFAULT_HEADERS[aiohttp.hdrs.ACCEPT_ENCODING] = _gen_accept_encoding_header()  # type: ignore
+try:
+    # Support brotli if installed
+    aiohttp.client_reqrep.ClientRequest.DEFAULT_HEADERS[aiohttp.hdrs.ACCEPT_ENCODING] = _gen_accept_encoding_header()  # type: ignore
+except Exception:
+    # aiohttp does it for us anyway
+    pass
 
 
 class _FakeResponse: