Resolve #3344504 "2.0 test failures"

Closes #3344504

src/Plugin/views/style/Table.php

@@ -537,7 +537,7 @@ class Table extends ViewsTable {
         // $aggr_values is indexed by group value and/or 'column'.
         // 'column' is the last evaluated value for the field.
         if (isset($aggr_values['column'])) {
-          $field_handlers[$field_name]->last_render = $aggr_values['column'];
+          $field_handlers[$field_name]->last_render = (string) $aggr_values['column'];
         }
         foreach ($aggr_values as $group => $value) {
           // 'column' function is last so may override earlier value.