Submission Review Guidelines:

• I have followed the WooCommerce Contributing Guidelines and the WordPress Coding Standards.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have reviewed my code for security best practices.
• Following the above guidelines will result in quick merges and clear and detailed feedback when appropriate.

Changes proposed in this Pull Request:

This PR fixes the scrolling of the editor and sidebar in the description modal editor.

Before:

After:

Closes #39189.

How to test the changes in this Pull Request:

Using the WooCommerce Testing Instructions Guide, include your detailed testing instructions:

1. Enable the new product editor.
2. Create a new product.
3. Click "Edit description".
4. Verify that the editor canvas (the "white block area") extends the full height of the modal.
5. Enter a description longer than will fit on the screen.
6. Verify that the editor can scroll.
7. Select a block.
8. Verify that the sidebar showing the block properties can be scroll if necessary.

Changelog entry

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