Fix width of Template Parts view (#50836)

Author: mirka

packages/edit-site/src/components/list/style.scss

@@ -33,6 +33,7 @@
 
 .edit-site {
 	.edit-site-list {
+		flex-grow: 1;
 		background: $white;
 		border-radius: $radius-block-ui * 4;
 		box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.8), 0 8px 10px -6px rgba(0, 0, 0, 0.8);