Twenty Nineteen: Add border-radius to avatar images in the editor.

This ensures that avatars design in the Post Author or Avatar blocks in the editor matches the front end.

Props pitamdey, shailu25, poena, sabernhardt, balub, sarath.ar, nicolefurlan, harshgajipara, pooja1210.
Fixes #59285.

git-svn-id: https://develop.svn.wordpress.org/trunk@57579 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-content/themes/twentynineteen/style-editor.css

@@ -1605,3 +1605,9 @@ ul.wp-block-archives li ul,
   padding-right: 0;
   width: 100%;
 }
+
+/** === Post Author Block === */
+.avatar,
+.wp-block-post-author__avatar img {
+  border-radius: 100%;
+}

src/wp-content/themes/twentynineteen/style-editor.scss

@@ -1021,3 +1021,10 @@ $group-block-background__padding: $font__size_base;
 		width: 100%;
 	}
 }
+
+/** === Post Author Block === */
+
+.avatar,
+.wp-block-post-author__avatar img {
+	border-radius: 100%;
+}