Use venv instead of virtualenv in test_installation

This eliminates the test dependency on virtualenv by using the
standard library venv module instead in test_installation.

test-requirements.txt

@@ -6,4 +6,3 @@ pre-commit
 pytest
 pytest-cov
 pytest-sugar
-virtualenv

test/test_installation.py

@@ -4,6 +4,8 @@
 import ast
 import os
 import subprocess
+import sys
+
 from git.compat import is_win
 from test.lib import TestBase
 from test.lib.helper import with_rw_directory
@@ -12,7 +14,7 @@
 class TestInstallation(TestBase):
     def setUp_venv(self, rw_dir):
         self.venv = rw_dir
-        subprocess.run(["virtualenv", self.venv], stdout=subprocess.PIPE)
+        subprocess.run([sys.executable, "-m", "venv", self.venv], stdout=subprocess.PIPE)
         bin_name = "Scripts" if is_win else "bin"
         self.python = os.path.join(self.venv, bin_name, "python")
         self.pip = os.path.join(self.venv, bin_name, "pip")