Fix false positives for prefers-contrast in media-feature-name-no-unk…

…nown (#5428)

* Added prefers-contrast media query

This is a new media query added to CSS Media Queries Level 5 to utilize the contrast preference operating systems provide.

Closes #5427

lib/reference/keywordSets.js

@@ -608,6 +608,7 @@ keywordSets.mediaFeatureNames = uniteSets(keywordSets.deprecatedMediaFeatureName
 	'overflow-inline',
 	'pointer',
 	'prefers-color-scheme',
+	'prefers-contrast',
 	'prefers-reduced-motion',
 	'prefers-reduced-transparency',
 	'resolution',