fixes differences api request test by doing object comparison

frontend/app/component/form/differences/DifferencesForm.test.tsx

@@ -2,7 +2,7 @@
  * @vitest-environment jsdom
  */
 
-import { overrideOnce, render, screen, fireEvent } from "app/test/unit";
+import { overrideOnce, render, screen, fireEvent, getUrlMethodAndBody } from "app/test/unit";
 import { userEvent } from "@testing-library/user-event";
 import { describe, expect, test, vi, afterEach } from "vitest";
 
@@ -221,13 +221,11 @@ describe("Test DifferencesForm", () => {
       const submitButton = screen.getByRole("button", { name: "Volgende" });
       await user.click(submitButton);
 
-      expect(spy).toHaveBeenCalledWith("http://testhost/v1/api/polling_stations/1/data_entries/1", {
-        method: "POST",
-        body: JSON.stringify(expectedRequest),
-        headers: {
-          "Content-Type": "application/json",
-        },
-      });
+      expect(spy).toHaveBeenCalled();
+      const { url, method, body } = getUrlMethodAndBody(spy.mock.calls);
+      expect(url).toEqual("http://testhost/v1/api/polling_stations/1/data_entries/1");
+      expect(method).toEqual("POST");
+      expect(body).toEqual(expectedRequest);
 
       const result = await screen.findByTestId("result");
       expect(result).toHaveTextContent(/^Success$/);