DiscountCondition\IsInCategory: Use integers instead of strings

Author: adriendupuis

docs/api/rest_api/rest_api_reference/input/examples/discounts/POST/DiscountCreate.json.example

@@ -22,7 +22,7 @@
         "conditions": [
             {
                 "class": "Ibexa\\Discounts\\Value\\DiscountCondition\\IsInCategory",
-                "parameters": [["1", "2"]]
+                "parameters": [[1, 2]]
             }
         ]
     }

docs/api/rest_api/rest_api_reference/input/examples/discounts/identifier/PATCH/DiscountUpdate.json.example

@@ -4,7 +4,7 @@
         "conditions": [
             {
                 "class": "Ibexa\\Discounts\\Value\\DiscountCondition\\IsInCategory",
-                "parameters": [["1", "3"]]
+                "parameters": [[1, 3]]
             }
         ]
     }