[CSS Modules] Add non-constructable stylesheet to Open Issues (#1264)

Adding additional open issue

Author: KurtCattiSchmidt

ShadowDOM/explainer.md

@@ -939,6 +939,7 @@ The following table compares pros and cons of the various proposals:
 * What happens in scenarios that cross document boundaries, such as `Document.parseHTMLUnsafe`?
 * How can developers check for and polyfill `shadowrootadoptedstylesheets`, given that the template element disappears from the DOM?
 * Is it possible to define an intentional race between an async preload of an external stylesheet and a just-in-time definition of a declarative module and only apply the one that wins? This might not be possible due to the fact that specifiers are unique.
+* How should this proposal work if non-constructable stylesheets are adopted for `adoptedstylesheets`? See https://github.com/w3c/csswg-drafts/issues/10013.
 
 ## References and acknowledgements
 Many thanks for valuable feedback and advice from other contributors: