Fix regression with columns appender (#6237)

This fixes an issue where the default appender in columns would have a border, and the wrong font. This was introduced as part of the input style consistency PR. Increasing selector specificity fixes this.

editor/components/default-block-appender/style.scss

@@ -1,7 +1,7 @@
 $empty-paragraph-height: $text-editor-font-size * 4;
 
 .editor-default-block-appender {
-	.editor-default-block-appender__content {
+	input[type=text].editor-default-block-appender__content { // needs specificity
 		border: none;
 		background: none;
 		box-shadow: none;