Update specificity of text color declaration

Block level global styling for cover block text colors were being overridden by default colors. This is because, for global styles, we were setting styles on the top-level cover block element. The default text color, however, was being set on the child cover block inner container.

Since the text content's nearest ancestor was the inner container, it was inheriting the inner containers text color declarations.

packages/block-library/src/cover/style.scss

@@ -11,6 +11,7 @@
 	padding: 1em;
 	// This block has customizable padding, border-box makes that more predictable.
 	box-sizing: border-box;
+	color: $white;
 
 	&.has-parallax {
 		background-attachment: fixed;
@@ -104,7 +105,6 @@
 	.wp-block-cover__inner-container {
 		width: 100%;
 		z-index: z-index(".wp-block-cover__inner-container");
-		color: $white;
 	}
 
 	p,