Add WebOb urljoin

Author: jackwalkerlabs

stubs/WebOb/webob/util.pyi

@@ -2,6 +2,7 @@ from collections.abc import Callable
 from typing import AnyStr
 
 def html_escape(s: object) -> str: ...
+def urljoin(base: str, url: str | None) -> str: ...
 def header_docstring(header: str, rfc_section: str) -> str: ...
 def warn_deprecation(text: str, version: str, stacklevel: int) -> None: ...