Unbreak <syntaxhighlight enclose="none">
It was always "none" and not "span", this must've been an accidental change.
Also add a CSS tweak to better render the common pattern of
<code><syntaxhighlight enclose="none">...</syntaxhighlight></code>.
Bug: T85794
Change-Id: I3ed1b7f3c954374b49fc9a97881ea5236415cb6f