dynamic cleanup: wrap local variable in switch with {}

* improves code consistency
* allows to add new case at the end

c++/src/capnp/dynamic.c++

@@ -563,7 +563,7 @@ void DynamicStruct::Builder::set(StructSchema::Field field, const DynamicValue::
                  .set(value.as<AnyPointer>());
           return;
 
-        case schema::Type::INTERFACE:
+        case schema::Type::INTERFACE: {
           auto interfaceType = type.asInterface();
           auto capability = value.as<DynamicCapability>();
           KJ_REQUIRE(capability.getSchema().extends(interfaceType), "Value type mismatch.") {
@@ -573,6 +573,7 @@ void DynamicStruct::Builder::set(StructSchema::Field field, const DynamicValue::
               kj::mv(capability.hook));
           return;
         }
+      }
 
       KJ_UNREACHABLE;
     }
@@ -742,7 +743,7 @@ void DynamicStruct::Builder::adopt(StructSchema::Field field, Orphan<DynamicValu
           }
           break;
 
-        case schema::Type::INTERFACE:
+        case schema::Type::INTERFACE: {
           auto interfaceType = type.asInterface();
           KJ_REQUIRE(orphan.getType() == DynamicValue::CAPABILITY &&
                      orphan.interfaceSchema.extends(interfaceType),
@@ -751,6 +752,7 @@ void DynamicStruct::Builder::adopt(StructSchema::Field field, Orphan<DynamicValu
           }
           break;
         }
+      }
 
       builder.getPointerField(slot.getOffset() * POINTERS).adopt(kj::mv(orphan.builder));
       return;