`Request` object behaves differently in fetch

### Link to the code that reproduces this issue https://github.com/lennartkerkvliet/next-fetch-request-bug ### To Reproduce When sending a request body using the `Request` object in a Next.js application while using server actions, the content-length parameter is not included in the request and instead chunked transfer encoding is used. This behavior differs from the expected functionality of the Fetch API, which internally is also constructing a `Request` object. Steps to reproduce the behavior: 1. Create a `Request` object with a body. 2. Pass the `Request` object to the `fetch` function. Example code: ```javascript const body = JSON.stringify({ username: "test", password: "password" }); const request = new Request("https://www.my-site.com/api/login", { method: "POST", headers: { "Content-Type": "application/json" }, body: body }); const response = await fetch(request); // Server receives an empty body ``` ### Current vs. Expected behavior I would expect the parameters in `Request` to be identical to when using the more traditional use of fetch API: ```javascript const body = JSON.stringify({ username: "test", password: "password" }); const response = await fetch("https://www.my-site.com/api/login", { method: "POST", headers: { "Content-Type": "application/json" }, body: body }); ``` but instead will return the latter <img width="1505" alt="Screenshot 2024-06-13 at 18 27 51" src="https://github.com/vercel/next.js/assets/5382580/39492428-d95d-412c-9683-5ddac824a7c9"> ### Provide environment information ```bash Operaring System: Arch: arm64 Version: macOS Sonoma 14.4.1 Binaries: Node: v22.2.0 npm: 10.7.0 Relevant Packages: next: 14.2.3 ``` ### Which area(s) are affected? (Select all that apply) Not sure, Runtime ### Which stage(s) are affected? (Select all that apply) next dev (local), Vercel (Deployed), Other (Deployed) ### Additional context - Using plain Node.js, the above code works as expected. It seems to be somewhat relat…