Fix Github refresh token error

It looks like they send JSON now!

httpx_oauth/clients/github.py

@@ -1,4 +1,3 @@
-import urllib.parse
 from typing import Any, Dict, List, Optional, Tuple, TypedDict, cast
 
 import httpx
@@ -97,12 +96,10 @@ async def refresh_token(self, refresh_token: str) -> OAuth2Token:
                 client, request, auth, exc_class=RefreshTokenError
             )
 
-            content_type = response.headers.get("content-type", "")
+            data = self.get_json(response, exc_class=RefreshTokenError)
 
             # GitHub sends errors with a 200 status code
-            # and a form-urlencoded content type 😕
-            if content_type.startswith("application/x-www-form-urlencoded"):
-                data = urllib.parse.parse_qs(response.text)
+            if "error" in data:
                 raise RefreshTokenError(cast(str, data["error"]), response)
 
             data = self.get_json(response, exc_class=RefreshTokenError)

tests/test_clients_github.py

@@ -1,5 +1,5 @@
+import json
 import re
-from urllib.parse import urlencode
 
 import pytest
 import respx
@@ -75,13 +75,12 @@ async def test_refresh_token_200_error(self):
             "error_description": "The refresh token passed is incorrect or expired.",
             "error_uri": "https://docs.github.com",
         }
-        error_response_encoded = urlencode(error_response)
 
         respx.post(client.refresh_token_endpoint).mock(
             return_value=Response(
                 200,
-                headers={"content-type": "application/x-www-form-urlencoded"},
-                content=error_response_encoded,
+                headers={"content-type": "application/json"},
+                content=json.dumps(error_response),
             )
         )