fix: update pluralization of yaml to non-disputable version

[morremeyer]

Changelog version

This PR updates the pluralization of YAML in an error message from „yamels“ to „yaml files“.

Long version

We were debugging an issue with failing git repository clones today. While doing so, the pluralization of „yaml“ to „yamels“ was bugging me extremely, so I thought about a version of it that was possibly agreeable to more people.

Therefore, I changed it to „yaml files“.

[hiddeco]

This PR erases signature history 😢

https://github.com/fluxcd/flux/search?q=yamel&type=Commits
https://github.com/fluxcd/flux/search?q=yamel+is%3Aissue&type=Issues
https://github.com/fluxcd/flux/search?q=yamel+is%3Aissue+is%3Apr&type=Issues

[shibumi]

This PR erases signature history

Well, everything beautiful needs a point where it starts. I would appreciate the term yaml files instead of yamels.

Why?

• When yaml files is used, it's clear that both parties (if human or not) talk about yaml
• yamels is confusing, when I had a look on this term the first time, I thought it's a new fancy file format or whatever (not kidding).

[hiddeco]

No worries, I do 100% understand the PR from a UX perspective.

Having known @squaremo for a while, I know both yamel and yamels are persistent in his vocabulary. I actually had a good laugh while Googling for "yamels" as squaremo/kubeyaml (the tool we use for replacing i.e. image tags while making image updates) is the only YAML related result on the first page.

[squaremo]

I bless this retro-corrective to my vocabulary