Fix issue of css affecting the nested accordion icon.

[levinbaria]

What?

Closes #71435

Fixes CSS selector affects the nested Accordion block icon.

Why?

The Accordion block can be nested, and in that some CSS selector affects the nested Accordion block icon.

How?

Made the CSS selector to apply only on the direct child only.

Testing Instructions

Insert an Accordion block.
Insert an additional Accordion block inside the Accordion panel.
Select the parent Accordion Content block.
Confirm that both toggle icons are rotated.

Testing Instructions for Keyboard

Screenshots or screencast

Before	After

[github-actions]

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Co-authored-by: levinbaria <levinbaria@git.wordpress.org>
Co-authored-by: t-hamano <wildworks@git.wordpress.org>

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[github-actions]

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[t-hamano]

Thanks for the PR!

For code readability, we can reuse the existing CSS selector. How about writing it like this?\

.wp-block-accordion-content.is-open {
	grid-template-rows: max-content 1fr;

	> .wp-block-accordion-header .accordion-content__toggle-icon.has-icon-plus {
		transform: rotate(45deg);
	}
}

[levinbaria]

Yes, that a good catch @t-hamano, I will update the CSS accordingly

[t-hamano]

LGTM!