HTML Block: Remove space below textarea (#70055)

Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

Author: t-hamano

packages/block-library/src/html/editor.scss

@@ -10,6 +10,7 @@
 	// The editing view for the HTML block is equivalent to block UI.
 	// Therefore we increase specificity to avoid theme styles bleeding in.
 	.block-editor-plain-text {
+		display: block;
 		box-sizing: border-box;
 		max-height: 250px;
 		@include editor-input-reset();