BP Nouveau: Improve sitewide notice display in 2022

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The icon background does not use the full height compared to other screen notices.

Here's the display without the patch applied:

Here's the display with the patch applied:

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In 13289:

BP Nouveau: Improve site-wide notice display in Twenty Twenty-Two

See #8718 (trunk)

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In 13290:

BP Nouveau: Improve site-wide notice display in Twenty Twenty-Two

Fixes #8718 (10.0 branch)