fix: chess readme env (#2016)

## Description
Change the env var to OPEN AI in readme

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## Type of change

Please check the options that are 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)
- [ ] Model update (Addition or modification of models)
- [x] Other (please describe): Typo fix

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## Checklist

- [x] Adherence to standards: Code complies with Agno’s style guidelines
and best practices.
- [x] Formatting and validation: You have run `./scripts/format.sh` and
`./scripts/validate.sh` to ensure code is formatted and linted.
- [x] Self-review completed: A thorough review has been performed by the
contributor(s).
- [ ] Documentation: Docstrings and comments have been added or updated
for any complex logic.
- [ ] Examples and guides: Relevant cookbook examples have been included
or updated (if applicable).
- [ ] Tested in a clean environment: Changes have been tested in a clean
environment to confirm expected behavior.
- [ ] Tests (optional): Tests have been added or updated to cover any
new or changed functionality.

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## Additional Notes

Include any deployment notes, performance implications, security
considerations, or other relevant information (e.g., screenshots or logs
if applicable).

cookbook/examples/apps/chess_team/README.md

@@ -27,7 +27,7 @@ pip install -r cookbook/examples/apps/chess_team/requirements.txt
 Create a `.envrc` file or export your API keys:
 
 ```shell
-export ANTHROPIC_API_KEY=your_api_key_here
+export OPENAI_API_KEY=your_api_key_here
 ```
 
 ### 4. Run the application