Preserve leading slashes in request path_url (#7315)

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Co-authored-by: Nate Prewitt <nate.prewitt@gmail.com>

Author: typhon8

src/requests/adapters.py

@@ -590,8 +590,6 @@ def request_url(
             using_socks_proxy = proxy_scheme.startswith("socks")
 
         url = request.path_url
-        if url.startswith("//"):  # Don't confuse urllib3
-            url = f"/{url.lstrip('/')}"
 
         if is_proxied_http_request and not using_socks_proxy:
             url = urldefragauth(request.url)

tests/test_adapters.py

@@ -1,8 +1,8 @@
 import requests.adapters
 
 
-def test_request_url_trims_leading_path_separators():
+def test_request_url_handles_leading_path_separators():
     """See also https://github.com/psf/requests/issues/6643."""
     a = requests.adapters.HTTPAdapter()
     p = requests.Request(method="GET", url="http://127.0.0.1:10000//v:h").prepare()
-    assert "/v:h" == a.request_url(p, {})
+    assert "//v:h" == a.request_url(p, {})