Less descriptive error message when `index` not in list item in Python 3.14

[DanielYang59]

Bug report

Bug description:

It looks like in Python 3.14 the error message became less descriptive when indexing a non-existent item in list:

>>> uv run -p 3.13 python -c '["a"].index(1)'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
    ["a"].index(1)
    ~~~~~~~~~~~^^^
ValueError: 1 is not in list

>>> uv run -p 3.14 python -c '["a"].index(1)'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
    ["a"].index(1)
    ~~~~~~~~~~~^^^
ValueError: list.index(x): x not in list

In 3.13 it's directly obvious 1 is not in list, and in Python 3.14 it refers to x where x is not even defined

CPython versions tested on:

3.14

Operating systems tested on:

macOS

[StanFromIreland]

See #116792 for why this will not be reverted, I closed as duplicate of an issue that seeks to further improve the current message.

[DanielYang59]

hi thanks for the input, sorry I didn't find those issue when searching