fix: #1834 minor error in docstring (#1837)

Author: seratch

src/agents/__init__.py

@@ -138,7 +138,7 @@
 
 
 def set_default_openai_key(key: str, use_for_tracing: bool = True) -> None:
-    """Set the default OpenAI API key to use for LLM requests (and optionally tracing(). This is
+    """Set the default OpenAI API key to use for LLM requests (and optionally tracing()). This is
     only necessary if the OPENAI_API_KEY environment variable is not already set.
 
     If provided, this key will be used instead of the OPENAI_API_KEY environment variable.