Fix Footnotes not saved if the Custom Fields panel is open

[shimotmk]

What?

fix #54653

Fix Footnotes not saved if the Custom Fields panel is open

I used this note as reference.
https://github.com/mburridge/gutenberg/blob/5e2df720ae89962df5ca8ce548846c1e1a6785ae/docs/how-to-guides/plugin-sidebar-0.md#note

Why?

How?

Testing Instructions

1. Open a post or page.
2. Open Custom Fields panel
3. setting footnotes and block.
4. You can confirm that it works as expected on both the management screen and the front screen.

Testing Instructions for Keyboard

Screenshots or screencast <!--

footnores.mp4

if applicable -->

[github-actions]

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Co-authored-by: shimotmk <[email protected]>
Co-authored-by: Mamaduka <[email protected]>
Co-authored-by: mrfoxtalbot <[email protected]>
Co-authored-by: Screenfeed <[email protected]>

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