fix(oas3): fix getting initial values for request body in OpenAPI 3.x (#9762)

Refs #9745

test/e2e-cypress/e2e/features/plugins/oas3/one-of-any-of-example.cy.js

@@ -0,0 +1,28 @@
+/**
+ * @prettier
+ */
+
+describe("OpenAPI 3.0 oneOf and anyOf example", () => {
+  it("should show example values for multipart/form-data and application/x-www-form-urlencoded content types", () => {
+    cy.visit("/?url=/documents/features/oas3-one-of-any-of-example.yaml").then(
+      () => {
+        cy.contains("/documentsWithCombineOneOf")
+          .click()
+          .get(".try-out__btn")
+          .click()
+          .get("textarea")
+          .contains("documentDate")
+          .should("exist")
+        cy.contains("/documentsWithCombineOneOf").click()
+        cy.contains("/documentsWithCombineAnyOf")
+          .click()
+          .get(".try-out__btn")
+          .contains("Try it out")
+          .click()
+          .get("textarea")
+          .contains("documentDate")
+          .should("exist")
+      }
+    )
+  })
+})