Include exception info when something goes wrong while refreshing tokens

```
An error occurred when refreshing user token: (invalid_request) Missing Code
```

is the message we're currently logging, that's not enough to do anything
with.

lib/galaxy/authnz/managers.py

@@ -340,9 +340,8 @@ class AuthnzManager:
             if refreshed:
                 log.debug(f"Refreshed user token via `{auth.provider}` identity provider")
             return True
-        except Exception as e:
-            msg = f"An error occurred when refreshing user token: {e}"
-            log.error(msg)
+        except Exception:
+            log.exception("An error occurred when refreshing user token")
             return False
 
     def refresh_expiring_oidc_tokens(self, trans, user=None):