Fix var --bs-body-font-family. Keep quotes in the font stack.

[cdaecke]

Description

Quotes in var --bs-body-font-family are removed.

Motivation & Context

When using something like $font-family-base: "Helvetica Neue", Arial the quotes are removed, so you will get this:

:root {
    --bs-body-font-family: Helvetica Neue, Arial;
}

Expected behaviour would be:

:root {
    --bs-body-font-family: "Helvetica Neue", Arial;
}

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

[ffoodd]

Most of the time, quotes are not needed, as Mathias Bynens explained a few years ago.

However if someone needs to use quotes, we should allow it. Thanks for the PR!