Extend typing for template_folder

Author: ivanovmg

src/flask/app.py

@@ -558,7 +558,7 @@ def __init__(
         static_host: t.Optional[str] = None,
         host_matching: bool = False,
         subdomain_matching: bool = False,
-        template_folder: t.Optional[str] = "templates",
+        template_folder: t.Optional[t.Union[str, os.PathLike]] = "templates",
         instance_path: t.Optional[str] = None,
         instance_relative_config: bool = False,
         root_path: t.Optional[str] = None,

src/flask/blueprints.py

@@ -250,7 +250,7 @@ def __init__(
         import_name: str,
         static_folder: t.Optional[t.Union[str, os.PathLike]] = None,
         static_url_path: t.Optional[str] = None,
-        template_folder: t.Optional[str] = None,
+        template_folder: t.Optional[t.Union[str, os.PathLike]] = None,
         url_prefix: t.Optional[str] = None,
         subdomain: t.Optional[str] = None,
         url_defaults: t.Optional[dict] = None,

src/flask/scaffold.py

@@ -93,7 +93,7 @@ def __init__(
         import_name: str,
         static_folder: t.Optional[t.Union[str, os.PathLike]] = None,
         static_url_path: t.Optional[str] = None,
-        template_folder: t.Optional[str] = None,
+        template_folder: t.Optional[t.Union[str, os.PathLike]] = None,
         root_path: t.Optional[str] = None,
     ):
         #: The name of the package or module that this object belongs