Fix requestBodyRequired (#5465) (#5466)

(cherry picked from commit 62d200f)

Co-authored-by: Quentin Pradet <quentin.pradet@elastic.co>

Author: github-actions[bot]

compiler/src/model/build-model.ts

@@ -286,6 +286,7 @@ function compileClassOrInterfaceDeclaration (declaration: ClassDeclaration | Int
 
       // validate body
       if (bodyMember != null) {
+        mapping.requestBodyRequired = !(bodyMember as PropertySignature).hasQuestionToken()
         assert(
           bodyMember,
           methods.some(method => ['POST', 'PUT', 'DELETE'].includes(method)),