Update dash/backend/registry.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: BSd3v

dash/backend/registry.py

@@ -15,10 +15,10 @@ def get_backend(name):
         module_name, class_name = _backend_imports[name.lower()]
         module = importlib.import_module(module_name)
         return getattr(module, class_name)
-    except KeyError:
-        raise ValueError(f"Unknown backend: {name}")
+    except KeyError as e:
+        raise ValueError(f"Unknown backend: {name}") from e
     except ImportError as e:
-        raise ImportError(f"Could not import module '{module_name}' for backend '{name}': {e}")
+        raise ImportError(f"Could not import module '{module_name}' for backend '{name}': {e}") from e
     except AttributeError as e:
-        raise AttributeError(f"Module '{module_name}' does not have class '{class_name}' for backend '{name}': {e}")
+        raise AttributeError(f"Module '{module_name}' does not have class '{class_name}' for backend '{name}': {e}") from e