Top toolbar: fix half a pixel artifacting of the bottom border. (#62225)

* Top toolbar: fix half a pixel artifacting of the bottom border.

* Address feedback.

* Restore previous fix after all.

* Use transparent background color.

* Update changelog.

* Move the rule to the right place.

* Remove entry from changelog.

Co-authored-by: jasmussen <joen@git.wordpress.org>
Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: draganescu <andraganescu@git.wordpress.org>
Co-authored-by: jeryj <jeryj@git.wordpress.org>

packages/editor/src/components/collapsible-block-toolbar/style.scss

@@ -7,6 +7,7 @@
 	.block-editor-block-contextual-toolbar {
 		border-bottom: 0;
 		height: 100%;
+		background: transparent;
 	}
 
 	// These rules ensure that icons are always positioned in a way that lines up with the rest of the icons in the toolbar.