Set integer type on tileSize (#8528)

Fixes an issue when setting tile size for custom map.

```
Error: sources.aaaaa.tileSize: number expected, string found
    at Object.Tn [as emitValidationErrors] (validate_style.js:37)
    at Ue (style.js:46)
    at i2._load (style.js:245)
    at style.js:235
```

api/src/database/system-data/fields/settings.yaml

@@ -320,6 +320,7 @@ fields:
               placeholder: http://{a-c}.tile.openstreetmap.org/{z}/{x}/{y}.png
         - field: tileSize
           name: $t:tile_size
+          type: integer
           schema:
             is_nullable: true
           meta: