More readable error message

[ftnext]

Description of the change

Error message style fix

Motivation

Thank you very much for developing this great library.
I saw the error message

  File "/.../venv/lib/python3.11/site-packages/google/generativeai/types/generation_types.py", line 328, in text
    raise ValueError(
ValueError: The `response.text` quick accessor only works for simple (single-`Part`) text responses. This response is not simple text.Use the `result.parts` accessor or the full `result.candidates[index].content.parts` lookup instead.

and found text.Use (no space!)

Type of change

Choose one: Other

Checklist

• I have performed a self-review of my code.
• I have added detailed comments to my code where applicable.
• I have verified that my change does not break existing code.
• My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• I am familiar with the Google Style Guide for the language I have coded in.
• I have read through the Contributing Guide and signed the Contributor License Agreement.

[MarkDaoust]

Thanks!