fix: nox.session.run-ing commands with pathlib.Path arguments

nox/command.py

@@ -71,8 +71,7 @@ def _clean_env(env: dict[str, str] | None) -> dict[str, str] | None:
 
 
 def _shlex_join(args: Sequence[str]) -> str:
-    # shlex.join() was added in Python 3.8
-    return " ".join(shlex.quote(arg) for arg in args)
+    return " ".join(shlex.quote(os.fspath(arg)) for arg in args)
 
 
 def run(

tests/test_command.py

@@ -22,6 +22,7 @@
 import subprocess
 import sys
 import time
+from pathlib import Path
 from textwrap import dedent
 from unittest import mock
 
@@ -112,6 +113,19 @@ def test_run_verbosity_failed_command(capsys, caplog):
     assert not logs
 
 
+@pytest.mark.skipif(
+    platform.system() == "Windows",
+    reason="See https://github.com/python/cpython/issues/85815",
+)
+def test_run_non_str():
+    result = nox.command.run(
+        [Path(PYTHON), "-c", "import sys; print(sys.argv)", Path(PYTHON)],
+        silent=True,
+    )
+
+    assert PYTHON in result
+
+
 def test_run_env_unicode():
     result = nox.command.run(
         [PYTHON, "-c", 'import os; print(os.environ["SIGIL"])'],