Closes https://github.com/zed-industries/zed/issues/34973

Fixes an issue where environment variables were not loaded when the
user's shell was tcsh and instead a file named `0` was dumped in the
current working directory with a copy of your environment variables as
json.

Follow-up to: 
- https://github.com/zed-industries/zed/pull/35002
- https://github.com/zed-industries/zed/pull/33599

Release Notes:

- Fixed a regression with loading environment variables in nushell