test: add workaround to fix failing grid-pro custom-field test (#9673)

Author: web-padawan

test/integration/grid-pro-custom-editor.test.js

@@ -22,6 +22,16 @@ describe('grid-pro custom editor', () => {
       </vaadin-gri-pro>
     `);
 
+    // FIXME: remove when switching to base styles.
+    // Ensure grid cells have some height.
+    fixtureSync(`
+      <style>
+        vaadin-grid-pro::part(cell) {
+          min-height: 36px;
+        }
+      </style>
+    `);
+
     const column = grid.querySelector(`[path="${path}"]`);
     switch (path) {
       case 'date':