Dangling attribute quote raises the wrong error message

[ianjosephwilson]

# missing closing "
node = html(t'<p class="{classes}></p>')

This fails saying the placeholder is not found which is not very helpful. I'm not sure if we are failing before a proper message or we need to detect it ourselves. Just putting this here so it gets dealt with at some point.

    def close(self) -> None:
        if self.stack:
            raise ValueError("Invalid HTML structure: unclosed tags remain.")
        if not self.placeholders.is_empty:
>           raise ValueError("Some placeholders were never resolved.")
E           ValueError: Some placeholders were never resolved.

tdom/parser.py:293: ValueError