Add quotes to variables in script

[bkmgit]

If this pull request addresses an open issue on the repository, please add 'Closes #NN' below, where NN is the issue number.

Closes #258

Please briefly summarise the changes made in the pull request, and the reason(s) for making these changes.

Make script and text consistent in using quotes and in having the same documentation

[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}.

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Rendered Changes

🔍 Inspect the changes: https://github.com/LibraryCarpentry/lc-shell/compare/md-outputs..md-outputs-PR-259

The following changes were observed in the rendered markdown documents:

 04-loops.md                   |  9 +++++----
 files/my_first_bash_script.sh | 12 +++++++-----
 md5sum.txt                    |  2 +-
 3 files changed, 13 insertions(+), 10 deletions(-)

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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.

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⏱️ Updated at 2024-04-03 12:05:42 +0000

[kaitlinnewson]

Small issue with formatting of this comment - doesn't match what is in the lesson

[kaitlinnewson]

Hi @bkmgit, thank you for this PR! I've made one small change request above - can you adjust this in your PR?