Luminance: Fix display of featured images

The featured images in Luminance were completely misaligned due to
changes in how Gutenberg has changed the specifity of style rules.
Rather than the custom block-specific CSS for the core/featured-image
block taking priority, the default block library styles did.

The problem has been reported upstream
(WordPress/gutenberg#64453) but in the
meantime, using the theme-wide custom CSS fixes the problem.

luminance/theme.json

@@ -507,9 +507,6 @@
 			"core/post-excerpt": {
 				"css": ".wp-block-post-excerpt .wp-block-post-excerpt__excerpt{line-height: inherit;}"
 			},
-			"core/post-featured-image": {
-				"css": ".wp-block-post-featured-image img{vertical-align:top;width: auto;}"
-			},
 			"core/post-navigation-link": {
 				"typography": {
 					"fontSize": "var(--wp--preset--font-size--small)",
@@ -794,7 +791,8 @@
 			"fontFamily": "var(--wp--preset--font-family--instrument-sans)",
 			"fontSize": "var(--wp--preset--font-size--medium)",
 			"lineHeight": "1.388888889"
-		}
+		},
+		"css": ".wp-block-post-featured-image img{vertical-align:top;width: auto;}"
 	},
 	"templateParts": [
 		{