Fix regex string literals to be raw strings which solves Syntax Error about the backslash escape character

[whitphx]

📚 Context

Fixes the following error.

 ❯ streamlit run data.text_column.py

  You can now view your Streamlit app in your browser.

  Local URL: http://localhost:8501
  Network URL: http://192.168.68.104:8501

  For better performance, install the Watchdog module:

  $ xcode-select --install
  $ pip install watchdog

/workspace/streamlit/docs/python/api-examples-source/data.text_column.py:24: SyntaxWarning: invalid escape sequence '\.'
  validate="^st\.[a-z_]+$",

🧠 Description of Changes

Revised:

Insert screenshot of your updated UI/code here

Current:

Insert screenshot of existing UI/code here

💥 Impact

Size:

• [x] Small
• [ ] Not small

🌐 References

• [ ] Notion

Contribution License Agreement

By submitting this pull request you agree that all contributions to this project are made under the Apache 2.0 license.

[sfc-gh-dmatthews]

Thanks @whitphx!