fix: change "have" to "has" in scale-to-zero warning

[bchaseUNB]

"container app" is singular, so use "has" instead of "have"

[prmerger-automator]

@bchaseUNB : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit ae0213e:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/container-apps/scale-app.md	✅Succeeded

For more details, please refer to the build report.

[Copilot]

Pull Request Overview

This PR corrects a grammatical error in the scale-to-zero warning message for Azure Container Apps documentation. The change ensures proper subject-verb agreement by changing "have" to "has" when referring to a singular "container app."

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[v-dirichards]

Looks good, thanks @bchaseUNB