fix(backend): happy-domを使用後にcloseするように (#14615)

* Add `DetachedWindowAPI.close` calls to `MfmService`

(cherry picked from commit ceaec3324925e53ca3f467b0438a98f1108eed0f)

* fix

* update changelog

* fix

---------

Co-authored-by: Julia Johannesen <julia@insertdomain.name>

packages/backend/src/core/MfmService.ts

@@ -239,7 +239,7 @@ export class MfmService {
 			return null;
 		}
 
-		const { window } = new Window();
+		const { happyDOM, window } = new Window();
 
 		const doc = window.document;
 
@@ -457,6 +457,10 @@ export class MfmService {
 
 		appendChildren(nodes, body);
 
-		return new XMLSerializer().serializeToString(body);
+		const serialized = new XMLSerializer().serializeToString(body);
+
+		happyDOM.close().catch(err => {});
+
+		return serialized;
 	}
 }