[3.14] gh-65697: Improved error msg for configparser key validation (GH-135527) (#135541)

gh-65697: Improved error msg for configparser key validation (GH-135527)

* Improved error msg for configparser key validation and added note in 3.14 whatsnew

* Properly added change to configparser

* 📜🤖 Added by blurb_it.

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(cherry picked from commit 81237fbcf6adc962647566eafca62dd5a905375e)

Co-authored-by: Jacob Austin Lincoln <99031153+lincolnj1@users.noreply.github.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>