fix ComonadEnv third law

[worldmaker18349276]

ex: https://try.purescript.org/?gist=82aad3725f27216aafcdfc51a65fd3c0

Description of the change

ComonadEnv third law is wrong. Duplicating env after local modification will remain modified. See above example.

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Checklist:

• [ ] Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• [ ] Linked any existing issues or proposals that this pull request should close
• [ ] Updated or added relevant documentation
• [ ] Added a test for the contribution (if applicable)