Theme:fix icon error of cascader and select (#15264)

packages/theme-chalk/src/cascader.scss

@@ -137,7 +137,7 @@
     @include m(extensible) {
       &:after {
         font-family: 'element-icons';
-        content: "\e604";
+        content: "\e6e0";
         font-size: 14px;
         color: rgb(191, 203, 217);
         position: absolute;

packages/theme-chalk/src/select-dropdown.scss

@@ -25,7 +25,7 @@
         position: absolute;
         right: 20px;
         font-family: 'element-icons';
-        content: "\E611";
+        content: "\e6da";
         font-size: 12px;
         font-weight: bold;
         -webkit-font-smoothing: antialiased;