fix: catch only JSON decode errors in error handling

nyacme/handlers/hetzner.py

@@ -40,7 +40,7 @@ class HetznerHandler(Handler):
             res = ex.fp.read().decode('utf-8')
             try:
                 raise Exception(json.loads(res)['error'])
-            except Exception:
+            except json.JSONDecodeError:
                 raise Exception(res)
 
     def create(self, record_name: str, record_value: str) -> None: