Use StillImage for emoji group header

Ref: grouped-emoji-picker

src/components/emoji_picker/emoji_picker.js

 import { defineAsyncComponent } from 'vue'
 import Checkbox from '../checkbox/checkbox.vue'
+import StillImage from '../still-image/still-image.vue'
 import lozad from 'lozad'
 import { library } from '@fortawesome/fontawesome-svg-core'
 import {
@@ -52,7 +53,8 @@ const EmojiPicker = {
   },
   components: {
     StickerPicker: defineAsyncComponent(() => import('../sticker_picker/sticker_picker.vue')),
-    Checkbox
+    Checkbox,
+    StillImage
   },
   methods: {
     onStickerUploaded (e) {

src/components/emoji_picker/emoji_picker.vue

@@ -16,10 +16,10 @@
             v-if="group.image"
             class="emoji-picker-header-image"
           >
-            <img
+            <still-image
               :alt="group.text"
               :src="group.image"
-            >
+            />
           </span>
           <FAIcon
             v-else