Widgets: Avoid an overflow issue in widget controls that include `<select>` form fields.

Props alexischenal, audrasjb, dkarfa.
Fixes #49401.

git-svn-id: https://develop.svn.wordpress.org/trunk@47365 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/widgets.css

@@ -607,6 +607,10 @@ div#widgets-right .closed .widgets-sortables {
 	background: #fff;
 }
 
+.widget-inside select {
+	max-width: 100%;
+}
+
 /* Dragging widgets over the available widget area show's a "Deactivate" message */
 #removing-widget {
 	display: none;