Fix left border of the first button in the gas price button group of the gas customization modal (#9406)

ui/app/components/app/gas-customization/gas-price-button-group/index.scss

@@ -219,6 +219,10 @@
     background: #f7fcff;
     border: 2px solid #2c8bdc;
 
+    &:first-child {
+      border: 2px solid #2c8bdc;
+    }
+
     .button-check-wrapper {
       height: 16px;
       width: 16px;