Fixes#5077
## Summary
Previously, in a powershell on windows when using `python -m ruff`
instead of `ruff` a call such as `python -m ruff "a b.py"` would fail
because the space would be split into two arguments.
The python docs
[recommend](https://docs.python.org/3/library/os.html#os.spawnv) using
subprocess instead of os.spawn variants, which does fix the problem.
## Test Plan
I manually confirmed that the problem previously occurred and now
doesn't anymore. This only happens in a very specific environment
(maturin build, windows, powershell), so i could try adding a step on CI
for it but i don't think it's worth it.
```
(.venv) PS C:\Users\Konstantin\PycharmProjects\ruff> python -m ruff "a b.py"
warning: Detected debug build without --no-cache.
error: Failed to lint a: The system cannot find the file specified. (os error 2)
error: Failed to lint b.py: The system cannot find the file specified. (os error 2)
a:1:1: E902 The system cannot find the file specified. (os error 2)
b.py:1:1: E902 The system cannot find the file specified. (os error 2)
Found 2 errors.
(.venv) PS C:\Users\Konstantin\PycharmProjects\ruff> python -m ruff "a b.py"
warning: Detected debug build without --no-cache.
a b.py:2:5: F841 [*] Local variable `x` is assigned to but never used
Found 1 error.
[*] 1 potentially fixable with the --fix option.
```
Prefer the version from a currently active virtualenv over a version
from `pip install --user`. Add the .exe extension on Windows, and
find the path for `pip install --user` correctly on Windows.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
