fixed Latte 3.1 compatibility (#1223)

Author: dg

src/templates/datagrid.latte

@@ -140,7 +140,7 @@
 						</th>
 					</tr>
 					<tr n:block="header-column-row">
-						<th n:snippet="thead-group-action" n:if="$hasGroupActions" n:attr="'rowspan=2' => !empty($filters) && !$control->hasOuterFilterRendering()" class="col-checkbox">
+						<th n:snippet="thead-group-action" n:if="$hasGroupActions" n:attr="rowspan => !empty($filters) && !$control->hasOuterFilterRendering() ? 2" class="col-checkbox">
 							<input n:if="$hasGroupActionOnRows" class="form-check-input" name="{$control->getFullName()|lower}-toggle-all" type="checkbox" data-check="{$control->getFullName()}" data-check-all="{$control->getFullName()}">
 						</th>
 						{foreach $columns as $key => $column}