[Windows] Basic run operation uses wrong environment

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Given this simple test:

```
def test_run(virtualenv):
import sys
cmd = ['python', '-c', 'import sys; print(sys.prefix)']
res = virtualenv.run(cmd, capture=True, text=True).strip()
assert sys.prefix not in res
```

This test runs a command in the virtualenv emitting the sys.prefix and expects it _not_ to be the sys.prefix of the test runner.

It passes on Unix-like OSs, but fails on Windows with this trace:

```
PS C:\Users\jaraco\draft> env/Scripts/pytest '\\vmware-host\shared folders\home\draft\virtualenv-run.py'
============================= test session starts =============================
platform win32 -- Python 3.8.3, pytest-6.0.1, py-1.9.0, pluggy-0.13.1
rootdir: \\vmware-host\shared folders\home\draft
plugins: shutil-1.7.0, virtualenv-1.7.0, xonsh-0.9.18
collected 1 item

\\vmware-host\shared folders\home\draft\virtualenv-run.py F [100%]

================================== FAILURES ===================================
__________________________________ test_run ___________________________________

virtualenv =

def test_run(virtualenv):
import sys
cmd = ['python', '-c', 'import sys; print(sys.prefix)']
res = virtualenv.run(cmd, capture=True, text=True).strip()
> assert sys.prefix not in res
E AssertionError: assert 'c:\\users\\...\\draft\\env' not in 'c:\\users\\...\\draft\\env'
E 'c:\\users\\jaraco\\draft\\env' is contained here:
E c:\users\jaraco\draft\env

\\vmware-host\shared folders\home\draft\virtualenv-run.py:5: AssertionError
---------------------------- Captured stdout setup ----------------------------
created virtual environment CPython3.8.3.final.0-64 in 703ms

creator CPython3Windows(dest=C:\Users\jaraco\AppData\Local\Temp\tmppmdecetw\.env, clear=False, global=False)

seeder FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=C:\Users\jaraco\AppData\Local\pypa\virtualenv)

added seed packages: pip==20.2.1, setuptools==49.2.1, wheel==0.34.2

activators BashActivator,BatchActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator

=========================== short test summary info ===========================
FAILED \\vmware-host\shared folders\home\draft\virtualenv-run.py::test_run - ...
============================== 1 failed in 1.23s ==============================
```

Start with the test_run reproduction in virtualenv-run.py and run it on Windows to confirm the failure. Trace the Windows path used by virtualenv.run and verify the command executes in the created virtual environment, then confirm the test passes.

Written by the indexing model from the issue text.