Fix typos in CSS classname

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

ee/app/assets/javascripts/feature_flags/components/environments_dropdown.vue

@@ -171,7 +171,7 @@ export default {
 <template>
   <div>
     <div class="dropdown position-relative">
-      <gl-icon name="search" class="seach-icon-input" />
+      <gl-icon name="search" class="search-icon-input" />
 
       <input
         type="text"

ee/app/assets/stylesheets/pages/feature_flags.scss

@@ -10,14 +10,14 @@ $label-blue: #428bca;
   background-color: $gray-300;
 }
 
-.seach-icon-input,
+.search-icon-input,
 .clear-search-input {
   position: absolute;
   z-index: 10;
   fill: $gray-300;
 }
 
-.seach-icon-input {
+.search-icon-input {
   left: 4px;
   top: 10px;
 }