fix: fix ssl behavior in request

- `ClientConnectionError` in `aiohttp` can wrap SSL handshake and
  certificate verification errors
- Retrying those hides the real cause and produced
  `TransientNetworkError` instead of the expected certificate error
- Removing `ClientConnectionError` from the transient list lets SSL
  errors surface correctly

vdirsyncer/http.py

@@ -268,7 +268,6 @@ async def request(
         except (
             ServerDisconnectedError,
             ServerTimeoutError,
-            ClientConnectionError,
             asyncio.TimeoutError,
         ) as e:
             # Retry only if the method is safe/idempotent for our DAV use