Order placeholders bug fix

[jbloomAus]

Description

Fixes self.order_placeholders to self.ordered_placeholders in MissionSpace.__eq__ Fixes #303

Type of change

Please delete options that are not relevant.

• [ x] 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

Screenshots

Not needed.

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Checklist:

• [x ] 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
• [x ] 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

Since it's a simple spelling mistake, it's not necessary to comment, edit documentation, or add or modify any tests.

[rodrigodelazcano]

Thanks @jbloomAus ! Actually, this PR solves the same issue as this one https://github.com/Farama-Foundation/Minigrid/pull/288 We didn't merge it because we would like to create a test. @jbloomAus Do you have the time to create this test in this PR?

[jbloomAus]

Hey @rodrigodelazcano,

All good. I've added a test for sync vectorization of environments. The test doesn't evaluate all registered Minigrid environments but enough to trigger the error before the fix which I think is pretty reasonable.

Is that sufficient for a merge?