CSS: postcss parser error fix

[louismaximepiton]

Description

Selected all ) * -, meaning a CSS variable is before a minus sign. Ref #37079.
Add a workflow to avoid forgetting it next times.

Motivation & Context

PostCSS potential errors

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

NA

Related issues

NA

[julien-deramond]

I've set up again the environment described in #36851 (comment) with our latest release, and there are no errors after executing NODE_ENV=production bin/webpack.

The errors mainly came from the use of CSS variables in calc() times a negative number. In this PR, the fix is not related to CSS variables. Are we sure it's needed?

[louismaximepiton]

Just tried this as well. Didn't manage to reproduce as well. Thanks for your time spent on the PR!