Use the standard library distutils for running tests

This is in line with what our unit tests are written with the assumption
of.

Author: pradyunsg

.github/workflows/ci.yml

@@ -42,7 +42,7 @@ jobs:
               - "src/pip/_vendor/**"
               - "pyproject.toml"
             tests:
-              # Anything that's touching testable stuff
+              # Anything that's touching code-related stuff
               - ".github/workflows/ci.yml"
               - "src/**"
               - "tests/**"

noxfile.py

@@ -110,7 +110,14 @@ def test(session: nox.Session) -> None:
     # Run the tests
     #   LC_CTYPE is set to get UTF-8 output inside of the subprocesses that our
     #   tests use.
-    session.run("pytest", *arguments, env={"LC_CTYPE": "en_US.UTF-8"})
+    session.run(
+        "pytest",
+        *arguments,
+        env={
+            "LC_CTYPE": "en_US.UTF-8",
+            "SETUPTOOLS_USE_DISTUTILS": "stdlib",
+        },
+    )
 
 
 @nox.session