Added f to format string

[uwagura]

Closes #6331 . Test not needed because I literally just added a character
Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• Changelog entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

Hi @uwagura and welcome to the Cylc community 🎉

Thanks for your bug report and many thanks for taking the time to fix the issue.

For legal reasons, we need all commit authors to enter their names into the CONTRIBURINTING.md file (no matter how small the fix) in order to agree to the CLA.

Make sure you write your name in the same format it appears in your commit (run git shortlog -se and copy your name as it appears there, or add an entry into the .mailmap file if you want it to appear differently).

(happy to forgo a changelog entry for this fix)

[uwagura]

@oliver-sanders , feels a bit strange to call myself a contributor for such a small change, but I've gone ahead and added myself to the contributors list and mailmap. I also added an entry to the changelog using towncrier, though I'm not entirely sure if I did it correctly. Let me know how how everything looks

[oliver-sanders]

It's a legal thing we have to do even with the smallest commits, we only need to do it once.

We greatly appreciate bugfixes, thanks for your contribution.