DEV: remove geopandas from the environment.yml file
- [x] closes #https://github.com/noatamir/pyladies-berlin-sprints/issues/9
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).

- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Thanks for working on this

@mroeschke you'd said you wanted the environment to enable people to run anything - should this single downstream test be removed? Hi @StefanieSenger - did you close this by accident? I think it looks right, I just wanted to double-check with Matthew whether we should also remove the downstream test or whether this is fine as-is @MarcoGorelli I must have, though I didn't realise I did ... I'd like to keep it open. Sorry, was my first ever open source contribution. Yeah I would be partial to be consistent and remove geopandas everywhere if we also want to remove it from the `environment.yml` for consistency (CI dependency files, unit tests, any ASVs, any doc reference) @StefanieSenger could you remove it from the environment.yml again? 

Additionally, you can delete the test ``test_geopandas`` in pandas/tests/test_downstream.py to get the ci passing. We can reopen the pr then Specifically for geopandas, I think we can indeed remove the test as well, and then the concern of not having all optional test dependencies installed is also gone (geopandas runs its CI with pandas main, so that should catch any potential compatibility issue relative fast as well). 

For the more general issue about other dependencies in little usage in environment.yml, I opened https://github.com/pandas-dev/pandas/issues/49998  
(removing geopandas from environment.yml won't actually remove it from the env, because it is also indirectly a dependency of pandas_gbq, another optional dependency only needed for a very few number of tests) @StefanieSenger if you want to reopen the PR, you will first have to "restore" the branch (there should be a button somewhere in the UI) Thanks for the instructions and the beginner friendly atmosphere. I will do this some time today.