fix parameter type (#37065)

Method Collection::duplicates() also accepts a string.

Author: nclavaud

src/Illuminate/Collections/Collection.php

@@ -260,7 +260,7 @@ public function diffKeysUsing($items, callable $callback)
     /**
      * Retrieve duplicate items from the collection.
      *
-     * @param  callable|null  $callback
+     * @param  callable|string|null  $callback
      * @param  bool  $strict
      * @return static
      */
@@ -288,7 +288,7 @@ public function duplicates($callback = null, $strict = false)
     /**
      * Retrieve duplicate items from the collection using strict comparison.
      *
-     * @param  callable|null  $callback
+     * @param  callable|string|null  $callback
      * @return static
      */
     public function duplicatesStrict($callback = null)

src/Illuminate/Collections/Enumerable.php

@@ -211,7 +211,7 @@ public function diffKeysUsing($items, callable $callback);
     /**
      * Retrieve duplicate items.
      *
-     * @param  callable|null  $callback
+     * @param  callable|string|null  $callback
      * @param  bool  $strict
      * @return static
      */
@@ -220,7 +220,7 @@ public function duplicates($callback = null, $strict = false);
     /**
      * Retrieve duplicate items using strict comparison.
      *
-     * @param  callable|null  $callback
+     * @param  callable|string|null  $callback
      * @return static
      */
     public function duplicatesStrict($callback = null);

src/Illuminate/Collections/LazyCollection.php

@@ -316,7 +316,7 @@ public function diffKeysUsing($items, callable $callback)
     /**
      * Retrieve duplicate items.
      *
-     * @param  callable|null  $callback
+     * @param  callable|string|null  $callback
      * @param  bool  $strict
      * @return static
      */
@@ -328,7 +328,7 @@ public function duplicates($callback = null, $strict = false)
     /**
      * Retrieve duplicate items using strict comparison.
      *
-     * @param  callable|null  $callback
+     * @param  callable|string|null  $callback
      * @return static
      */
     public function duplicatesStrict($callback = null)