fix(BaseStyles): remove unknown props from fallback when feature flag is enabled

[joshblack]

Update how we pass along system props in BaseStyles when the CSS Modules flag is enabled. Currently, when the flag is enabled we are still passing along color, fontFamily, and lineHeight to the underlying element. This change updates the component to use CSS Custom Properties as a bridge between what is provided as props and what is applied to the element in CSS.

Changelog

New

Changed

• Update BaseStyles to set common styles using CSS Custom Properties instead of as attributes on the element
• Update FeatureFlags to merge scope with parent context value

Removed

Rollout strategy

• Patch release

[changeset-bot]

🦋 Changeset detected

Latest commit: d9be714

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Patch

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	104.39 KB (-0.06% 🔽)
packages/react/dist/browser.umd.js	104.91 KB (+0.08% 🔺)

[francinelucca]

Noted the weight of the item titles changed in the VRT updates, intended?

[joshblack]

@francinelucca thanks for calling that out! Went to double-check and it seems like yes 👍 The current snapshots do not seem to be using the modern action list and it's probably because of the same bug with feature flags that I ran into 🤔

[primer-integration]

👋 Hi from github/github! Your integration PR is ready: https://github.com/github/github/pull/359710