docs(tutorials): fixed environment creation link

[lpizzinidev]

Description

The link at

Gymnasium/docs/tutorials/environment_creation.py

Line 23 in 8f0baf6

`the documentation of Gymnasium’s API </api/core>`__.

was redirecting to 404.

I changed it to redirect to https://gymnasium.farama.org/api/env/

Fixes #231

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• 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

[pseudo-rnd-thoughts]

Thanks for spotting that