text: Title: Page privacy model renders 2 headers and icons
  Body: <!--
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  ### Issue Summary
  Page privacy model renders 2 headers and icons when a parent page has been made private.
  ![image](https://github.com/wagtail/wagtail/assets/75799735/26ca0fb8-f086-4bb2-9e1d-78e1cd4517fc)
  
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  A summary of the issue.
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  ### Steps to Reproduce
  
  1. Set a page to private.
  2. Visit a child page and click change privacy
  
  Any other relevant information. For example, why do you consider this a bug and what did you expect to happen instead?
  
  I expect for only the second heading and icon to be displayed.
  -   I have confirmed that this issue can be reproduced as described on a fresh Wagtail project: yes
  
  ### Technical details
  
  -   Python version:  3.12
  -   Django version: 5.0.6
  -   Wagtail version: 6.2 (latest) and 6.1
  -   Browser version: You can use https://www.whatsmybrowser.org/ to find this out.
  
  ### Working on this
  
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