Update alert.mdx

[dar-b]

Changed chars to 128

Checklist

• [ ] Add meaningful unit tests for your component (verify that all lines are covered)
• [ ] Verify that all existing tests pass
• [ ] Add component features demo in Storybook (different stories)
• [ ] Approve test images for new stories
• [ ] Add screenshots of the key elements of the component

[CLAassistant]

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