Relax test_list_installed_deps() to allow other packages (#2796)

Relax the check in `test_list_installed_deps()` to allow `pip freeze`
to return other packages before `pip`.  This is necessary
if the Python interpreter vendors some packages itself, so that they
are available even in fresh venv.  This is the case e.g. for cffi
in PyPy.

docs/changelog/2796.misc.rst

@@ -0,0 +1,3 @@
+Relax the assertion in ``test_list_installed_deps`` to allow packages
+other than ``pip`` to be present in the fresh venv, to fix tests
+on PyPy.

tests/tox_env/python/test_python_api.py

@@ -186,6 +186,6 @@ def test_list_installed_deps(in_ci: bool, tox_project: ToxProjectCreator, mocker
     mocker.patch("tox.tox_env.python.api.is_ci", return_value=in_ci)
     result = tox_project({"tox.ini": "[testenv]\nskip_install = true"}).run("r", "-e", "py")
     if in_ci:
-        assert "py: pip==" in result.out
+        assert "pip==" in result.out
     else:
-        assert "py: pip==" not in result.out
+        assert "pip==" not in result.out