fix(backend): happy-domで外部HTMLをパースする際に関連リソースが読み込まれる問題を修正 (#14521)

* bump happy-dom, disable all JS&c when parsing

version 10 didn't quite support disabling all of that

I have tested that `MfmService` (the other code that uses `happy-dom`)
still works fine: the RSS feed for a user is generated correctly, with
HTML rendered from MFM

(cherry picked from commit 26e0412fbb91447c37e8fb06ffb0487346063bb8)

* Update Changelog

* lint

* fix possible memory leak

---------

Co-authored-by: dakkar <dakkar@thenautilus.net>

packages/backend/package.json

@@ -119,7 +119,7 @@
 		"fluent-ffmpeg": "2.1.3",
 		"form-data": "4.0.0",
 		"got": "14.4.2",
-		"happy-dom": "10.0.3",
+		"happy-dom": "15.6.1",
 		"hpagent": "1.2.0",
 		"htmlescape": "1.1.1",
 		"http-link-header": "1.1.3",