gh-102856: Add missing quote to fix doctest

[hugovk]

Document: whatsnew/3.12
-----------------------
**********************************************************************
File "whatsnew/3.12.rst", line ?, in default
Failed example:
    f"This is the playlist: {", ".join(songs)}"
Expected:
    'This is the playlist: Take me back to Eden, Alkaline, Ascensionism
Got:
    'This is the playlist: Take me back to Eden, Alkaline, Ascensionism'
**********************************************************************
1 items had failures:
   1 of  12 in default
12 tests in 1 items.
11 passed and 1 failed.
***Test Failed*** 1 failures.

https://github.com/python/cpython/actions/runs/5066957137/jobs/9097400760

Introduced in #104824.

[miss-islington]

Thanks @hugovk for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[bedevere-bot]

GH-104854 is a backport of this pull request to the 3.12 branch.