[networking] Respect `SSLKEYLOGFILE` environment variable (#9543)

Authored by: luiso1979

yt_dlp/networking/_helper.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import contextlib
 import functools
+import os
 import socket
 import ssl
 import sys
@@ -121,6 +122,9 @@ def make_ssl_context(
     context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
     context.check_hostname = verify
     context.verify_mode = ssl.CERT_REQUIRED if verify else ssl.CERT_NONE
+    # OpenSSL 1.1.1+ Python 3.8+ keylog file
+    if hasattr(context, 'keylog_filename'):
+        context.keylog_filename = os.environ.get('SSLKEYLOGFILE')
 
     # Some servers may reject requests if ALPN extension is not sent. See:
     # https://github.com/python/cpython/issues/85140