Unhelpful traceback (`OpenSSL.SSL.Error`) when certificate problems arise

This issue has been migrated from [#15058](https://github.com/matrix-org/synapse/issues/15058).

---

**Required logs**
```
Traceback (most recent call last):
File "/root/matrix-backend-repo/riot-matrix/synapse/synapse/http/[server.py](http://server.py/)", line 368, in _async_render_wrapper
callback_return = await self._async_render(request)
File "/root/matrix-backend-repo/riot-matrix/synapse/synapse/http/[server.py](http://server.py/)", line 574, in _async_render
callback_return = await raw_callback_return
File "/root/matrix-backend-repo/riot-matrix/synapse/synapse/rest/client/[login.py](http://login.py/)", line 653, in on_POST
body = await self._http_client.post_raw(uri, args)
File "/root/matrix-backend-repo/riot-matrix/synapse/synapse/http/[client.py](http://client.py/)", line 499, in post_raw
response = await self.request(
File "/root/matrix-backend-repo/riot-matrix/synapse/synapse/http/[client.py](http://client.py/)", line 444, in request
response = await make_deferred_yieldable(request_deferred)
twisted.web._newclient.RequestTransmissionFailed: []
```