Changing style block description

[benazeer-ben]

What?

Fixes #43668

Why?

Wording in the style block description is confusing as per the ticket details.

How?

Changed the wording of the description as per the suggestion in ticket.

Testing Instructions

Go to site editor.
Check global style settings.
Verify the change in the description.

Screenshots or screencast

Before	After

[github-actions]

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Co-authored-by: benazeer-ben <benazeer@git.wordpress.org>
Co-authored-by: masperber <masperber@git.wordpress.org>

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[github-actions]

Warning: Type of PR label mismatch

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• Labels found: [Focus] Accessibility (a11y), Global Styles.

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[github-actions]

Warning: Type of PR label mismatch

To merge this PR, it requires exactly 1 label indicating the type of PR. Other labels are optional and not being checked here.

• Type-related labels to choose from: [Type] Automated Testing, [Type] Breaking Change, [Type] Bug, [Type] Build Tooling, [Type] Code Quality, [Type] Copy, [Type] Developer Documentation, [Type] Enhancement, [Type] Experimental, [Type] Feature, [Type] New API, [Type] Task, [Type] Technical Prototype, [Type] Performance, [Type] Project Management, [Type] Regression, [Type] Security, [Type] WP Core Ticket, Backport from WordPress Core, Gutenberg Plugin.
• Labels found: [Focus] Accessibility (a11y), Global Styles.

Read more about Type labels in Gutenberg. Don't worry if you don't have the required permissions to add labels; the PR reviewer should be able to help with the task.