ColorPalette: Fix transparent checkered background pattern

[brookewp]

What?

Update the ColorPalette component's transparent checkered background pattern, so it doesn't become slightly cut off on the right side as outlined in this issue: #42687

Why?

For a more visually appealing look.

One thing to note is in Storybook, the background is 248px wide when set to the WP Sidebar max-width. In the editor, it's 228px wide, so the look is slightly different the checkered pattern is still cut off but in a less awkward way.

If we don't want anything cut off, we could change the pattern to 19px and set the height from 64px to 57px. For one example, so visually, it doesn't change too much.

How?

By changing the background size and positioning to 24px instead of 25px, as suggested by @mirka in the issue mentioned above (#42687).

Testing Instructions

1. Add a block that has color options (i.e. button block, paragraph block) to the editor in a page or post
2. Click on 'Background', 'Text', 'Link', or whichever color options are available in the block sidebar
3. See the transparent background with the checkered pattern that isn't as cut off on the right side as the 'before' screenshot below

Screenshots or screencast

Before:

After:

[chad1008]

LGTM! 🚀 🚢

[ciampo]

Probably better if we add a CHANGELOG entry for this fix?