Docs: fix .order values in the migration guide

[julien-deramond]

Description

While answering to #41029, I spotted a tiny error in our migration guide.

We also have .order-0:

bootstrap/dist/css/bootstrap.css

Lines 7871 to 7901 in cbbb567

	.order-first {
	order: -1 !important;
	}
	.order-0 {
	order: 0 !important;
	}
	.order-1 {
	order: 1 !important;
	}
	.order-2 {
	order: 2 !important;
	}
	.order-3 {
	order: 3 !important;
	}
	.order-4 {
	order: 4 !important;
	}
	.order-5 {
	order: 5 !important;
	}
	.order-last {
	order: 6 !important;
	}

And it was already the case in Bootstrap v5.0.0 (source: https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.css)

Type of changes

• Docs fix (non-breaking change which fixes an issue)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• (N/A) I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-41030--twbs-bootstrap.netlify.app/docs/5.3/migration/