Fixed yii\grid\GridView::guessColumns() to work with numeric column names

Closes #10580

framework/CHANGELOG.md

@@ -49,6 +49,7 @@ Yii Framework 2 Change Log
 - Bug #10385: Fixed `yii\validators\CaptchaValidator` passed incorrect hashKey to JS validator when `captchaAction` begins with `/` (silverfire)
 - Bug #10467: Fixed `yii\di\Instance::ensure()` to work with minimum settings (LAV45)
 - Bug #10541: Fixed division by zero issue in `Console` helper progress bar (youmad)
+- Bug #10580: Fixed `yii\grid\GridView::guessColumns()` to work with numeric column names (silverfire)
 - Bug: Fixed generation of canonical URLs for `ViewAction` pages (samdark)
 - Bug: Fixed `mb_*` functions calls to use `UTF-8` or `Yii::$app->charset` (silverfire)
 - Enh #3506: Added `yii\validators\IpValidator` to perform validation of IP addresses and subnets (SilverFire, samdark)

framework/grid/GridView.php

@@ -569,7 +569,7 @@ class GridView extends BaseListView
         $model = reset($models);
         if (is_array($model) || is_object($model)) {
             foreach ($model as $name => $value) {
-                $this->columns[] = $name;
+                $this->columns[] = (string) $name;
             }
         }
     }