html5lib: Fix type alias (#11480)

Pretty sure this is what I meant to write in the first place.

Fixes #11478

Author: JelleZijlstra

stubs/html5lib/html5lib/_inputstream.pyi

@@ -11,7 +11,7 @@ class _Encoding(Protocol):
 
 _UnicodeInputStream: TypeAlias = str | SupportsRead[str]
 _BinaryInputStream: TypeAlias = bytes | SupportsRead[bytes]
-_InputStream: TypeAlias = _UnicodeInputStream  # noqa: Y047  # used in other files
+_InputStream: TypeAlias = _UnicodeInputStream | _BinaryInputStream  # noqa: Y047  # used in other files
 
 spaceCharactersBytes: Any
 asciiLettersBytes: Any