Update semantic-layer-6-advanced-metrics.md (#4789)

## What are you changing in this pull request and why?
Fix indent and incorrect filter and measure in `Ratio metrics` which are
causing errors in implementing the code:
```sql
 - name: food_revenue
    description: The revenue from food in each order.
    label: Food Revenue
    type: simple
    type_params:
      measure: revenue
      filter: |
        {{ Dimension('order__is_food_order') }} = true
```
to
```
 - name: food_revenue
   description: The revenue from food in each order.
   label: Food Revenue
   type: simple
   type_params:
     measure: food_revenue
```

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website/docs/best-practices/how-we-build-our-metrics/semantic-layer-6-advanced-metrics.md

@@ -21,13 +21,11 @@ We're not limited to just passing measures through to our metrics, we can also _
 
 ```YAML
  - name: food_revenue
-    description: The revenue from food in each order.
-    label: Food Revenue
-    type: simple
-    type_params:
-      measure: revenue
-      filter: |
-        {{ Dimension('order__is_food_order') }} = true
+   description: The revenue from food in each order.
+   label: Food Revenue
+   type: simple
+   type_params:
+     measure: food_revenue
 ```
 
 - 📝 Now we can set up our ratio metric.