Fix: Add missing quotes in lists.md solution

[Aditee-18]

Closes #154

This PR corrects a syntax error in the solution for the "Fill in the Blank" exercise in episodes/lists.md. The closing single quotes were missing from two f-strings, as noted in the issue.

[github-actions]

Thank you!

Thank you for your pull request 😃

🤖 This automated message can help you check the rendered files in your submission for clarity. If you have any questions, please feel free to open an issue in {sandpaper}.

If you have files that automatically render output (e.g. R Markdown), then you should check for the following:

• 🎯 correct output
• 🖼️ correct figures
• ❓ new warnings
• ‼️ new errors

Rendered Changes

🔍 Inspect the changes: https://github.com/LibraryCarpentry/lc-python-intro/compare/md-outputs..md-outputs-PR-155

The following changes were observed in the rendered markdown documents:

 lists.md   | 4 ++--
 md5sum.txt | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

What does this mean?

If you have source files that require output and figures to be generated (e.g. R Markdown), then it is important to make sure the generated figures and output are reproducible.

This output provides a way for you to inspect the output in a diff-friendly manner so that it's easy to see the changes that occur due to new software versions or randomisation.

⏱️ Updated at 2025-09-18 15:47:09 +0000

[chennesy]

Thanks @Aditee-18! Fixes #155