Upgrade vendored distro to use new typing and API

The most recent version of distro, 1.6.0, include type information. This
allows pip to remove some workarounds. See upstream commit:
python-distro/distro@20cb68d

The new version also deprecated the top level function
distro.linux_distribution(). Switch to the new preferred API. See
upstream commit:
python-distro/distro@f947776

Author: jdufresne

news/c8285e11-5b65-498c-9eaa-85ca096243f9.vendor.rst

@@ -0,0 +1 @@
+Upgrade distro to 1.6.0.

pyproject.toml

@@ -51,6 +51,7 @@ drop = [
 [tool.vendoring.typing-stubs]
 six = ["six.__init__", "six.moves.__init__", "six.moves.configparser"]
 appdirs = []
+distro = []
 
 [tool.vendoring.license.directories]
 setuptools = "pkg_resources"

src/pip/_internal/network/session.py

@@ -2,16 +2,6 @@
 network request configuration and behavior.
 """
 
-# When mypy runs on Windows the call to distro.linux_distribution() is skipped
-# resulting in the failure:
-#
-#     error: unused 'type: ignore' comment
-#
-# If the upstream module adds typing, this comment should be removed. See
-# https://github.com/nir0s/distro/pull/269
-#
-# mypy: warn-unused-ignores=False
-
 import email.utils
 import ipaddress
 import json
@@ -128,9 +118,8 @@ def user_agent() -> str:
     if sys.platform.startswith("linux"):
         from pip._vendor import distro
 
-        # https://github.com/nir0s/distro/pull/269
-        linux_distribution = distro.linux_distribution()  # type: ignore
-        distro_infos = dict(
+        linux_distribution = distro.name(), distro.version(), distro.codename()
+        distro_infos: Dict[str, Any] = dict(
             filter(
                 lambda x: x[1],
                 zip(["name", "version", "id"], linux_distribution),