Inaccessible DERP when using https_proxy

### What is the issue?

Tested on both fedora 40 and macos sonoma, that when proxying through socks5 using the https_proxy variable, DERP servers are not reachable and shows "not connected to HOME derp region ".

Tailscale netcheck works perfectly fine probably because it uses icmp (guess), but for some reason, proxying https over devices that can communicate with derp by themselves is broken.

Breaks NAT-port negotation as well, so devices with no port forwarding break

### Steps to reproduce

do a socks5 proxy with ssh and add the local port to the https_proxy variable under your installation's environment file

### Are there any recent changes that introduced the issue?

_No response_

### OS

Linux, macOS

### OS version

Fedora 40, Sonoma

### Tailscale version

1.68.1

### Other software

_No response_

### Bug report

_No response_