Fix field example value

Author: pedrosousa

src/content/docs/ruleset-engine/rules-language/fields/http-request-body.mdx

@@ -74,7 +74,7 @@ The return value may be truncated if [`http.request.body.truncated`](#httpreques
 
 Example value:
 
-`{username": ["admin"]}`
+`{"username": ["admin"]}`
 
 Example: