[BUG] markdownShortcutPlugin ignores allowedHeadingLevels setting

[kraus-milan]

• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• I have read the documentation and cannot find an answer.

Describe the bug

markdownShortcutPlugin reads allowedHeadingLevels$ in init, but headingsPlugin updates the setting only in update, so markdownShortcutPlugin always allows default levels of headers (all) and ignores custom allowedHeadingLevels