🐛 BUG: Proxy environment variables didn't work.

### Which Cloudflare product(s) does this pertain to?

Wrangler core, Miniflare

### What version(s) of the tool(s) are you using?

3.17.1

### What version of Node are you using?

18.16.0

### What operating system are you using?

Linux

### Describe the Bug

When debugging locally, I need to make the fetch go through a proxy, but during actual testing, I found out that it is not going through the proxy.

```
❯ uname -a
Linux youxam-Ubuntu 6.2.0-37-generic #38~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Nov 2 18:01:13 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

❯ cat worker.ts
export interface Env {
}

export default {
async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise {
const ip = await fetch("https://ipinfo.io/json?token=c31843916e5fd7")
console.log(await ip.json())
return new Response('Hello World!');
},
};

❯ https_proxy=http://127.0.0.1:7890 curl https://ipinfo.io/json\?token\=c31843916e5fd7
{
"ip": "124.244.179.246",
"hostname": "124244179246.ctinets.com",
"city": "Hong Kong",
"region": "Central and Western",
"country": "HK",
"loc": "22.2783,114.1747",
"org": "AS9269 Hong Kong Broadband Network Ltd.",
"timezone": "Asia/Hong_Kong"
}

❯ https_proxy=http://127.0.0.1:7890 wrangler dev
Proxy environment variables detected. We'll use your proxy for fetch requests.
⛅️ wrangler 3.17.1
-------------------
⎔ Starting local server...
[mf:inf] Ready on http://*:8787
[mf:inf] - http://127.0.0.1:8787
[mf:inf] - http://10.117.253.152:8787
[mf:inf] - http://localhost:8787
[mf:inf] - http://[::1]:8787
{
ip: 'xxx.xxx.xxx.xxx',
city: 'Beijing',
region: 'Beijing',
country: 'CN',
loc: 'xxx',
org: 'xxx',
timezone: 'Asia/Shanghai'
}
```

### Please provide a link to a minimal reproduction

_No response_

### Please provide any relevant error logs

_No response_