[css-content] doesn't include C.2.86 from CSS2.1

[Loirooriol]

CSS2.1 added this text (C.2.86):

A 'close-quote' that would make the depth negative is in error and is
ignored (at rendering time): the depth stays at 0 and no quote mark is
rendered (although the rest of the 'content' property's value is still
inserted).

You can see it in https://www.w3.org/TR/CSS21/generate.html#quotes-insert

But this is not in https://drafts.csswg.org/css-content/#quote-values

[fantasai]

Fixed in 95a6e40 , closing as duplicate of #2038