added support for boolean keys in Collection::groupBy method

The following PR adds support for boolean keys when used in ``groupBy`` method of ```\lluminate\Support\Collection``. Related to #18672 problem.

src/Illuminate/Support/Collection.php

@@ -546,6 +546,10 @@ public function groupBy($groupBy, $preserveKeys = false)
             }
 
             foreach ($groupKeys as $groupKey) {
+                if (is_bool($groupKey)) {
+                    $groupKey = (int) $groupKey;
+                }
+
                 if (! array_key_exists($groupKey, $results)) {
                     $results[$groupKey] = new static;
                 }