Resolve warnings with Sass 1.59.3

Resolve warnings in tint-color and shade-color.

Description

When using tint-color or shade-color triggers the following warning:

    ╷
212 │   @return mix(black, $color, $weight);
    │           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ╵
    node_modules/bootstrap/scss/_functions.scss 212:11  shade-color()
    src/style/index.scss 90:37                          root stylesheet

Deprecation Warning: $weight: Passing a number without unit % (20) is deprecated.

To preserve current behavior: $weight * 1%

More info: https://sass-lang.com/d/function-units

The issue stems from newer sass versions deprecating variable passing without a unit and this PR just adds units.

Motivation & Context

Every time I build a project I get a several warnings if I have used tint-color or shade-color.

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

• https://deploy-preview-{your_pr_number}--twbs-bootstrap.netlify.app/

Related issues

Same root cause as https://github.com/twbs/bootstrap/pull/37425