Update thumbnail.html

Author: in-session

app/code/Magento/Ui/view/base/web/templates/grid/cells/thumbnail.html

@@ -6,6 +6,6 @@
 -->
 <span class="thumbnail-container">
     <span class="thumbnail-wrapper">
-        <img class="admin__control-thumbnail" attr="src: $col.getSrc($row()), alt: $col.getAlt($row())"/>
+        <img class="admin__control-thumbnail" attr="src: $col.getSrc($row()), alt: $col.getAlt($row())" loading="lazy"/>
     </span>
 </span>