.venv created even if there's no py file

The venv creation happens even if there's no python file (e.g it will fail)

```C#
#:package Aspire.Hosting.Python@13.1.0-*
#:package Aspire.Hosting.JavaScript@13.1.0-*
#:sdk Aspire.AppHost.Sdk@13.1.0-*

var builder = DistributedApplication.CreateBuilder(args);

builder.AddPythonApp("job1", ".", "app.py");

builder.Build().Run();
```

You don't need an app.py, but a venv will be created.