Quote block's deletion doesn't persist

[hypest]

Description

Trying to delete a Quote block by backspacing, removes the block from the editor but the block is still there in "Code editor" mode. I'd expect the block to not be there after backspacing it.

Originally spotted on the mobile app but we then noticed that it happens on the web clients too.

Step-by-step reproduction instructions

1. Run Gutenberg off a merged PR like this one: http://m62bf9dp.gutenberg.run/wp-admin/post-new.php
2. Add a quote block. (it's fine to leave it empty)
3. Add a paragraph block after the Quote block and type in a couple of characters
4. Focus the Quote block input
5. Hit backspace to delete the Quote block
6. Switch to "Code editor" mode from the 3-dot menu on the top-right
7. Notice the Quote block's markup still being there 💥

Screenshots, screen recording, code snippet

quote_wont_delete_web.mov

Environment info

• Gutenberg off trunk b6f0bdf
• Browser: Firefox 93.0

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[fluiddot]

I think this might be related to the changes introduced in #34241, I tried to reproduce this issue using the previous commit (d8808e8) of the PR merge commit (39806aa) in trunk, and the issue didn't happen.

cc @youknowriad