refactor: improve blacklisted username error by adding secondary message (#3444)

tests/api.test.js

@@ -291,7 +291,9 @@ describe("Test /api/", () => {
     await api(req, res);
 
     expect(res.setHeader).toBeCalledWith("Content-Type", "image/svg+xml");
-    expect(res.send).toBeCalledWith(renderError("Something went wrong"));
+    expect(res.send).toBeCalledWith(
+      renderError("Something went wrong", "This username is blacklisted"),
+    );
   });
 
   it("should render error card when wrong locale is provided", async () => {