typo error in _security_secret.py

[Bijon Guha]

 warnings.warn(
     f"ENVIRONMENT VARIABLE 'FASTAPI_SIMPLE_SECURITY_SECRET' NOT FOUND\n"
     f"\tGenerated a single-use secret key for this session:\n"
     f"\t{SECRET=}"

)

[Tolki]

Could you be a bit clearer as to what the typo is?