fix: align yaml option with documentation

docs/examples/with-multiple-requests.md

@@ -2,7 +2,7 @@
 
 First, create a resource:
 
-```http #createUser,format=yaml
+```http #createUser,yaml,json
 POST https://httpbin.org/post
 Content-Type: application/json
 

src/execution/handlers/handlers.http.ts

@@ -44,7 +44,7 @@ const httpHandler: ExecutionHandler = ({
       );
 
       let parsedBody = body;
-      if (options.format === 'yaml') {
+      if (options.yaml) {
         try {
           const parsed = YAML.parse(body);
           parsedBody = JSON.stringify(parsed);