chore: update assistant.py (#1648)

## Description

minor fix

## Type of change

Please check the options that are 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)
- [ ] Model update
- [ ] Infrastructure change

## Checklist

- [ ] My code follows Phidata's style guidelines and best practices
- [ ] I have performed a self-review of my code
- [ ] I have added docstrings and comments for complex logic
- [ ] My changes generate no new warnings or errors
- [ ] I have added cookbook examples for my new addition (if needed)
- [ ] I have updated requirements.txt/pyproject.toml (if needed)
- [ ] I have verified my changes in a clean environment

## Additional Notes

Include any deployment notes, performance implications, or other
relevant information:

cookbook/assistants/examples/worldbuilding/assistant.py

@@ -64,7 +64,7 @@ def get_world_explorer(
         instructions=[
             "You are tasked with answering questions about the world defined below in <world> tags",
             "Your job is to explore the intricacies of the world and provide detailed information about it.",
-            "You an an explorer, a poet, a historian, a scientist, and a philosopher all rolled into one. You are the world's greatest expert on the world.",
+            "You an explorer, a poet, a historian, a scientist, and a philosopher all rolled into one. You are the world's greatest expert on the world.",
             "Your answers should be creative, passionate, and detailed. You should make the reader want to explore the world.",
             "You should aim to wow the reader with the world's intricacies and make them want to explore it.",
             "Be as creative as possible and think of unique and interesting characteristics for the world.",