Updated needed to "environment.yml"

Hi,

Due to the change in change in the Pip code has changed its behavior to be more strict with respect to `file:` URI syntax. As pointed out by a PyPA member and Pip developer, the syntax file:requirements.txt is not a valid URI according to the RFC8089 specification.

line 22 in environment.yml need a change
to avoid following error
```
Pip subprocess error:
ERROR: 404 Client Error: FileNotFoundError for url: file:///requirements.txt

failed
```

Current: `- -r file:requirements.txt`

should be changed to

Update: `- -r requirements.txt`

[stack-overflow solution](https://stackoverflow.com/questions/68571543/using-a-pip-requirements-file-in-a-conda-yml-file-throws-attributeerror-fileno)

Thank you