Fix type hint of BaseEngine.template_dirs (#1954)

Author: Viicos

django-stubs/template/backends/base.pyi

@@ -16,7 +16,7 @@ class BaseEngine:
     def from_string(self, template_code: str) -> _EngineTemplate: ...
     def get_template(self, template_name: str) -> _EngineTemplate: ...
     @cached_property
-    def template_dirs(self) -> tuple[str]: ...
+    def template_dirs(self) -> tuple[str, ...]: ...
     def iter_template_filenames(self, template_name: str) -> Iterator[str]: ...
 
 @type_check_only