Update _floating-labels.scss

[jonnysp]

Closes #37330

Description

Motivation & Context

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

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
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• Before https://twbs-bootstrap.netlify.app/docs/5.2/forms/floating-labels/

• After https://deploy-preview-37359--twbs-bootstrap.netlify.app/docs/5.2/forms/floating-labels/

Related issues

[mdo]

Closing for #37299.