docs: fix description of update cart OAS (#11278)

www/apps/api-reference/specs/store/openapi.full.yaml

@@ -694,7 +694,7 @@ paths:
     post:
       operationId: PostCartsId
       summary: Update a Cart
-      description: Update a cart's details. This unsets the shipping an payment methods chosen before, and the customer would have to choose them again.
+      description: Update a cart's details. This unsets the payment methods chosen before, and the customer would have to choose them again. Also, if the customer has chosen a shipping method whose option isn't valid for the cart's shipping address anymore, the shipping method will be unset. For example, if the shipping option is valid only in the US geo zone, and the shipping address's country code is `DE`, the shipping method will be unset.
       x-authenticated: false
       parameters:
         - name: id

www/apps/api-reference/specs/store/paths/store_carts_{id}.yaml

@@ -68,8 +68,12 @@ post:
   operationId: PostCartsId
   summary: Update a Cart
   description: >-
-    Update a cart's details. This unsets the shipping an payment methods chosen
-    before, and the customer would have to choose them again.
+    Update a cart's details. This unsets the payment methods chosen before, and
+    the customer would have to choose them again. Also, if the customer has
+    chosen a shipping method whose option isn't valid for the cart's shipping
+    address anymore, the shipping method will be unset. For example, if the
+    shipping option is valid only in the US geo zone, and the shipping address's
+    country code is `DE`, the shipping method will be unset.
   x-authenticated: false
   parameters:
     - name: id