test: update DOM snapshots for grid header and footer slots

Updated the DOM snapshot tests to reflect the new header and footer slot
elements that were added to the grid component structure.

Part of #986

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: Artur-

packages/grid/test/dom/__snapshots__/grid.test.snap.js

@@ -42,6 +42,13 @@ snapshots["vaadin-grid shadow default"] =
   id="scroller"
   style="touch-action: none;"
 >
+  <div
+    id="gridHeader"
+    part="header"
+  >
+    <slot name="header">
+    </slot>
+  </div>
   <table
     aria-colcount="2"
     aria-multiselectable="true"
@@ -248,6 +255,13 @@ snapshots["vaadin-grid shadow default"] =
       </tr>
     </tfoot>
   </table>
+  <div
+    id="gridFooter"
+    part="footer"
+  >
+    <slot name="footer">
+    </slot>
+  </div>
   <div part="reorder-ghost">
   </div>
 </div>
@@ -266,6 +280,13 @@ snapshots["vaadin-grid shadow selected"] =
   id="scroller"
   style="touch-action: none;"
 >
+  <div
+    id="gridHeader"
+    part="header"
+  >
+    <slot name="header">
+    </slot>
+  </div>
   <table
     aria-colcount="2"
     aria-multiselectable="true"
@@ -473,6 +494,13 @@ snapshots["vaadin-grid shadow selected"] =
       </tr>
     </tfoot>
   </table>
+  <div
+    id="gridFooter"
+    part="footer"
+  >
+    <slot name="footer">
+    </slot>
+  </div>
   <div part="reorder-ghost">
   </div>
 </div>
@@ -491,6 +519,13 @@ snapshots["vaadin-grid shadow details opened"] =
   id="scroller"
   style="touch-action: none;"
 >
+  <div
+    id="gridHeader"
+    part="header"
+  >
+    <slot name="header">
+    </slot>
+  </div>
   <table
     aria-colcount="2"
     aria-multiselectable="true"
@@ -697,6 +732,13 @@ snapshots["vaadin-grid shadow details opened"] =
       </tr>
     </tfoot>
   </table>
+  <div
+    id="gridFooter"
+    part="footer"
+  >
+    <slot name="footer">
+    </slot>
+  </div>
   <div part="reorder-ghost">
   </div>
 </div>
@@ -716,6 +758,13 @@ snapshots["vaadin-grid shadow hidden column"] =
   scrolling=""
   style="touch-action: none;"
 >
+  <div
+    id="gridHeader"
+    part="header"
+  >
+    <slot name="header">
+    </slot>
+  </div>
   <table
     aria-colcount="2"
     aria-multiselectable="true"
@@ -870,6 +919,13 @@ snapshots["vaadin-grid shadow hidden column"] =
       </tr>
     </tfoot>
   </table>
+  <div
+    id="gridFooter"
+    part="footer"
+  >
+    <slot name="footer">
+    </slot>
+  </div>
   <div part="reorder-ghost">
   </div>
 </div>
@@ -889,6 +945,13 @@ snapshots["vaadin-grid shadow hidden column selected"] =
   scrolling=""
   style="touch-action: none;"
 >
+  <div
+    id="gridHeader"
+    part="header"
+  >
+    <slot name="header">
+    </slot>
+  </div>
   <table
     aria-colcount="2"
     aria-multiselectable="true"
@@ -1044,6 +1107,13 @@ snapshots["vaadin-grid shadow hidden column selected"] =
       </tr>
     </tfoot>
   </table>
+  <div
+    id="gridFooter"
+    part="footer"
+  >
+    <slot name="footer">
+    </slot>
+  </div>
   <div part="reorder-ghost">
   </div>
 </div>