Fixes Pyright type errors for src/flask/blueprint.py

CHANGES.rst

@@ -6,6 +6,7 @@ Version 3.1.0
 -   ``Flask.open_resource``/``open_instance_resource`` and
     ``Blueprint.open_resource`` take an ``encoding`` parameter to use when
     opening in text mode. It defaults to ``utf-8``. :issue:`5504`
+-   Fixes Pyright type errors in ``src/flask/blueprint.py``. :issue:`5545`
 
 Version 3.0.3
 -------------

src/flask/blueprints.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import os
 import typing as t
 from datetime import timedelta
+from io import BufferedReader
 
 from .cli import AppGroup
 from .globals import current_app
@@ -103,7 +104,7 @@ class Blueprint(SansioBlueprint):
 
     def open_resource(
         self, resource: str, mode: str = "rb", encoding: str | None = "utf-8"
-    ) -> t.IO[t.AnyStr]:
+    ) -> t.IO[t.AnyStr] | BufferedReader:
         """Open a resource file relative to :attr:`root_path` for reading. The
         blueprint-relative equivalent of the app's :meth:`~.Flask.open_resource`
         method.