requests 2.32.3 & urllib3 1.26.18 issue with unicode put

I'm building requests 2.32.3 in Fedora Linux and I have a problem with test_unicode_header_name - the test hangs.

It's reproducible - when I use urllib3 at least 2.0.2, the code works fine, with urllib3 1.26.18, it hangs waiting for a response.

Expected Result

Older urllib3 is still allowed (urllib3>=1.21.1,<3) so it should work.

Actual Result

The call to requests.put hangs and if killed, the stacktrace is:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/lbalhar/Software/requests/src/requests/api.py", line 130, in put
    return request("put", url, data=data, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/lbalhar/Software/requests/src/requests/api.py", line 59, in request
    return session.request(method=method, url=url, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/lbalhar/Software/requests/src/requests/sessions.py", line 589, in request
    resp = self.send(prep, **send_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/lbalhar/Software/requests/src/requests/sessions.py", line 703, in send
    r = adapter.send(request, **kwargs)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/lbalhar/Software/requests/src/requests/adapters.py", line 667, in send
    resp = conn.urlopen(
           ^^^^^^^^^^^^^
  File "/home/lbalhar/.virtualenvs/requests/lib/python3.12/site-packages/urllib3/connectionpool.py", line 715, in urlopen
    httplib_response = self._make_request(
                       ^^^^^^^^^^^^^^^^^^^
  File "/home/lbalhar/.virtualenvs/requests/lib/python3.12/site-packages/urllib3/connectionpool.py", line 467, in _make_request
    six.raise_from(e, None)
  File "<string>", line 3, in raise_from
  File "/home/lbalhar/.virtualenvs/requests/lib/python3.12/site-packages/urllib3/connectionpool.py", line 462, in _make_request
    httplib_response = conn.getresponse()
                       ^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/http/client.py", line 1428, in getresponse
    response.begin()
  File "/usr/lib64/python3.12/http/client.py", line 331, in begin
    version, status, reason = self._read_status()
                              ^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/http/client.py", line 292, in _read_status
    line = str(self.fp.readline(_MAXLINE + 1), "iso-8859-1")
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/socket.py", line 707, in readinto
    return self._sock.recv_into(b)
           ^^^^^^^^^^^^^^^^^^^^^^^
KeyboardInterrupt

Reproduction Steps

Start httpbin instance, install urllib3<2 and then:

import requests
requests.put("http://127.0.0.1:8080/put", headers={"Content-Type": "application/octet-stream"}, data="\xff")

System Information

$ python -m requests.help

{
  "chardet": {
    "version": null
  },
  "charset_normalizer": {
    "version": "3.3.2"
  },
  "cryptography": {
    "version": ""
  },
  "idna": {
    "version": "3.7"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.12.3"
  },
  "platform": {
    "release": "6.8.10-300.fc40.x86_64",
    "system": "Linux"
  },
  "pyOpenSSL": {
    "openssl_version": "",
    "version": null
  },
  "requests": {
    "version": "2.32.3"
  },
  "system_ssl": {
    "version": "30200010"
  },
  "urllib3": {
    "version": "1.26.18"
  },
  "using_charset_normalizer": true,
  "using_pyopenssl": false
}

Start with test_unicode_header_name and reproduce the hang against a local httpbin instance using urllib3 1.26.18 and a newer 2.x version. Trace the request through requests/api.py, sessions.py, and adapters.py, then add or adjust coverage so the documented PUT completes with the supported urllib3 range.