Chunked upload fails when using HTTP proxy

Not sure whether this is actually a `requests` bug, but trying here first as it's here it manifests.

I'm using a http proxy for https traffic, and it works fine for normal GET, POST and PUT requests using `requests`. However, if enabled chunked uploads, it fails with `requests.exceptions.ConnectionError: [SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1131)`

From googling it appears to be trying to access the http proxy using https. I'm fully aware of the normal "problem" where people confuse the protocols and use "https://" for their http proxy, but as can be seen in the example below this is not the problem in this case. 

I've been digging into `adapters.py` and the `low_conn` connection it uses _appears_ to have the correct proxy set (with "http" as protocol), but this is outside my expertise.

## Expected Result

Request to go through proxy like for non-chunked uploads without errors.

## Actual Result

```
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/dist-packages/requests/adapters.py", line 521, in send
    low_conn.endheaders()
  File "/usr/lib/python3.8/http/client.py", line 1251, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1011, in _send_output
    self.send(msg)
  File "/usr/lib/python3.8/http/client.py", line 951, in send
    self.connect()
  File "/usr/local/lib/python3.8/dist-packages/urllib3/connection.py", line 414, in connect
    self.sock = ssl_wrap_socket(
  File "/usr/local/lib/python3.8/dist-packages/urllib3/util/ssl_.py", line 449, in ssl_wrap_socket
    ssl_sock = _ssl_wrap_socket_impl(
  File "/usr/local/lib/python3.8/dist-packages/urllib3/util/ssl_.py", line 493, in _ssl_wrap_socket_impl
    return ssl_context.wrap_socket(sock, server_hostname=server_hostname)
  File "/usr/lib/python3.8/ssl.py", line 500, in wrap_socket
    return self.sslsocket_class._create(
  File "/usr/lib/python3.8/ssl.py", line 1040, in _create
    self.do_handshake()
  File "/usr/lib/python3.8/ssl.py", line 1309, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLError: [SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1131)
```

## Reproduction Steps

Run script below with and without proxy. Without proxy it works fine, with http proxy it gives above error.

```python
import requests

with open('test', 'w') as f:
    f.write('test')

with open('test', 'rb') as f:
    resp = requests.put('https://www.google.com', data=f)
    assert resp.status_code == 405

def x():
    yield "test".encode('utf-8')

resp = requests.put('https://www.google.com', data=x())
assert resp.status_code == 405
```

## System Information

    $ python -m requests.help

```json
{
  "chardet": {
    "version": null
  },
  "charset_normalizer": {
    "version": "3.0.1"
  },
  "cryptography": {
    "version": ""
  },
  "idna": {
    "version": "3.4"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.8.10"
  },
  "platform": {
    "release": "4.18.0-425.10.1.el8_7.x86_64",
    "system": "Linux"
  },
  "pyOpenSSL": {
    "openssl_version": "",
    "version": null
  },
  "requests": {
    "version": "2.28.2"
  },
  "system_ssl": {
    "version": "1010106f"
  },
  "urllib3": {
    "version": "1.26.14"
  },
  "using_charset_normalizer": true,
  "using_pyopenssl": false
}
```

I did look first but missed the other issue. This is a duplicate of https://github.com/psf/requests/issues/6279