Fix IssueLabelToken treating alternative light schemes as dark

[iansan5653]

The IssueLabelToken conditionally picks colors based on whether colorScheme === 'light'. This strategy assumes that there exist only two color schemes, when in reality there are many.

The fix for this is to use resolvedColorMode, which has four possible values: dark, night, light, and day (it's not clear what the difference between dark and night or light and day are, but this is what the value is typed as). So instead, to accurately determine whether the color scheme is a light one, we can see if resolvedColorMode is light or day.

Update: instead of using resolvedColorMode we decided to use resolvedColorTheme and see if it startsWith the expected color mode. This is less robust to new theme name formats but somewhat safer because there is no guarantee that the color mode actually matches the theme in real life, and the theme is what really determines the colors that are rendered.

Alternatively, we could instead call colorScheme.includes('light'), but I avoided this solution because it feels fragile (not robust to the possibility of future themes that are named differently.

Closes #3098

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After:

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🦋 Changeset detected

Latest commit: 6390d9f

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

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@primer/react	Patch

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[colebemis]

Thanks for the quick fix ⚡

[github-actions]

size-limit report 📦

Path	Size
dist/browser.esm.js	95.09 KB (+0.03% 🔺)
dist/browser.umd.js	95.63 KB (+0.03% 🔺)

[broccolinisoup]

Thanks! 🚀 Just missing a changeset.