Fix typo in EnvironmentCreation tutorial

[elliottower]

Description

Very minor fix, just updating the tutorial as mentioned in #881, to remove the agents from the environment when the game has terminated (otherwise it leads to issues with API tests, and it led them astray copying this incomplete example code).

Fixes #881

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have run pytest -v and no errors are present.
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I solved any possible warnings that pytest -v has generated that are related to my code to the best of my knowledge.
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[jjshoots]

LGTM