Columns block: Adding a column creates deprecations in the saved content

[gziolo]

Describe the bug

Discovered when testing #27681.

It was probably introduced in #24711.

There is this edge case when adding a new column in the Columns block updates child Column blocks with a number value for width attribute. In #24711 width was updated to work with percentage values (or strings? in general) so this triggers deprecation in the editor.

To reproduce
Steps to reproduce the behavior:

1. Create a new Blog Post
2. Add A Columns block
3. Select 70/30
4. Change column 1 to 90%
5. Set Column 2 to 10% (or around there)
6. Add the third column
7. Save the post
8. Refresh the page and observer JS consoler

Expected behavior

When the block is saved it uses with values for Column blocks that don't trigger deprecations.

Screenshots