Fix third-party issues found by stubtest (#6667)

stubs/beautifulsoup4/bs4/builder/_htmlparser.pyi

@@ -11,7 +11,7 @@ class BeautifulSoupHTMLParser(HTMLParser):
     on_duplicate_attribute: Any
     already_closed_empty_element: Any
     def __init__(self, *args, **kwargs) -> None: ...
-    def error(self, msg) -> None: ...
+    def error(self, msg: str) -> None: ...
     def handle_startendtag(self, name, attrs) -> None: ...
     def handle_starttag(self, name, attrs, handle_empty_element: bool = ...) -> None: ...
     def handle_endtag(self, name, check_already_closed: bool = ...) -> None: ...