Docs: update silenced SCSS deprecations for Vite

[Daniel15]

Description

Removes mixed-decls from and adds if-function to the list of silenced SCSS deprecations.

Motivation & Context

• There's ~78 violations of if-function
• Silencing mixed-decls now throws this warning:

Warning: mixed-decls deprecation is obsolete. If you were previously silencing it, your code may now behave in unexpected ways.

and removing it from the silenceDeprecations list works (no errors or warnings are output as a result).

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
• [N/A] 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
• [N/A] All new and existing tests passed

Live previews

• https://deploy-preview-42069--twbs-bootstrap.netlify.app/docs/5.3/getting-started/vite/#configure-vite

[julien-deramond]

Thanks for the PR @Daniel15

LGTM. This aligns with the config updates I recently made to the Vite example in our twbs/examples repository.

I am adding the "on-hold" label for now. We are currently prioritizing work on the v6-dev branch and pausing merges into main to simplify rebases. Once @mdo and I have finalized the synchronization process between these branches, we will move forward with this.