Reduce the padding around the sibling inserter icon so that the icon …

…doesn't interfere with other UI elements. Kind of fixes #16646. I wanted to try a delay on the inserter, but animating the display attribute in CSS isn't possible. I think that's why the Inserter uses the opacity instead, but opacity still takes up space even when opacity is set to 0.

packages/block-editor/src/components/block-list/style.scss

@@ -860,12 +860,12 @@
 
 	// Show a clickable plus.
 	.block-editor-inserter__toggle {
-		margin-top: -8px;
 		border-radius: 50%;
 		color: $blue-medium-focus;
 		background: $white;
-		height: $block-padding * 2 + 8px;
-		width: $block-padding * 2 + 8px;
+		height: $block-padding * 2;
+		width: $block-padding * 2;
+		padding: 4px;
 
 		&:not(:disabled):not([aria-disabled="true"]):hover {
 			box-shadow: none;