Linting/mypy fixes

Author: ianthomas23

lib/matplotlib/backend_bases.py

@@ -108,7 +108,8 @@ def _safe_pyplot_import():
         from matplotlib.backends.registry import backend_registry
         backend = backend_registry.backend_for_gui_framework(current_framework)
         if backend is None:
-            raise RuntimeError(f"No suitable backend for the current GUI framework {current_framework!r}")
+            raise RuntimeError("No suitable backend for the current GUI framework "
+                               f"{current_framework!r}")
 
         rcParams["backend"] = mpl.rcParamsOrig["backend"] = backend
         import matplotlib.pyplot as plt  # Now this should succeed.

lib/matplotlib/rcsetup.pyi

@@ -8,6 +8,8 @@ interactive_bk: list[str]
 non_interactive_bk: list[str]
 all_backends: list[str]
 
+def __dir__() -> list[str]: ...
+
 _T = TypeVar("_T")
 
 def _listify_validator(s: Callable[[Any], _T]) -> Callable[[Any], list[_T]]: ...