Keep media rename file extensions fixed

src/web/views/settings/media-library/list.hbs

@@ -100,6 +100,7 @@
     <label for="media-gallery-filename" class="form-label">Filename</label>
     <div class="input-group">
       <input id="media-gallery-filename" name="name" type="text" class="form-control" maxlength="255" required data-media-gallery-filename />
+      <span class="input-group-text" data-media-gallery-extension aria-label="File extension"></span>
       <button type="submit" class="btn btn-primary" title="Save filename" data-media-gallery-rename-save><i class="bi bi-floppy" aria-hidden="true"></i><span class="visually-hidden">Save filename</span></button>
     </div>
     <p class="small mb-0 mt-2" role="status" data-media-gallery-rename-status hidden></p>