[11.x] add nullOnUpdate() method to ForeignKeyDefinition (#52798)

* add nullOnUpdate() method to ForeignKeyDefinition

* Update ForeignKeyDefinition.php

---------

Co-authored-by: Taylor Otwell <[email protected]>

Author: gisuNasr

src/Illuminate/Database/Schema/ForeignKeyDefinition.php

@@ -34,6 +34,16 @@ public function restrictOnUpdate()
         return $this->onUpdate('restrict');
     }
 
+    /**
+     * Indicate that updates should set the foreign key value to null.
+     *
+     * @return $this
+     */
+    public function nullOnUpdate()
+    {
+        return $this->onUpdate('set null');
+    }
+
     /**
      * Indicate that updates should have "no action".
      *