[css-ruby-1][editorial] Gloss in-flow jargon (#13031)

Author: cvrebert

css-ruby-1/Overview.bs

@@ -318,7 +318,7 @@ Anonymous Ruby Box Generation</h3>
 
 	<ol>
 		<li id="anon-gen-inlinize"><strong>[=Inlinify=] block-level boxes:</strong>
-			Any in-flow boxes directly contained by a
+			Any [=in-flow=] boxes directly contained by a
 			[=ruby container=],
 			[=ruby base container=],
 			[=ruby annotation container=],