docs(material/button): avoid clipping icon (angular#30095)

Fixes that the container in the button example was too narrow and was clipping the button.

Fixes angular#30091.

Author: crisbeto

src/components-examples/material/button/button-overview/button-overview-example.css

@@ -27,5 +27,5 @@ section {
 .example-button-container {
   display: flex;
   justify-content: center;
-  width: 120px;
+  width: 140px;
 }