Do not enable venv in terminal for bash-like oneshot task invocations (#8444)

Release Notes:
- Work around #8334 by only activating venv in the terminal not in tasks
(see #8440 for a proper solution)
- To use venv modify your tasks in the following way:
```json
{
  "label": "Python main.py",
  "command": "sh",
  "args": ["-c", "source .venv/bin/activate && python3 main.py"]
}
```

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Co-authored-by: Kirill Bulatov <kirill@zed.dev>