windows: Don't load login shell environment (#22681)

I'm consistently getting the following error on startup:

```
2025-01-05T14:45:43.4602865+01:00 [ERROR] SHELL environment variable is not assigned so we can't source login environment variables

Caused by:
    environment variable not found
```

The source function, `load_login_shell_environment`, assumes a UNIX
environment and should therefore not be called on Windows. (Unless you
are using git bash?)

Release Notes:

* N/A