Fix schedule bug in nightly functional tests

[james-garriss]

🗣 Description

Set a default value for the email input.

💭 Motivation and context

Closes: #1389

🧪 Testing

Create a test repo to test the solution: https://github.com/james-garriss/test-schedule-inputs/tree/main

✅ Pre-approval checklist

• [x] This PR has an informative and human-readable title.
• [x] PR targets the correct parent branch (e.g., main or release-name) for merge.
• [x] Changes are limited to a single goal - eschew scope creep!
• [x] Changes are sized such that they do not touch excessive number of files.
• [x] These code changes follow the ScubaGear [content style guide]
• [x] Related issues these changes resolve are linked preferably via [closing keywords]
• [x] All relevant type-of-change labels added.
• [x] All relevant project fields are set.
• [x] All relevant repo and/or project documentation updated to reflect these changes.
• [x] All relevant functional tests passed.
• [x] All automated checks (e.g., linting, static analysis, unit/smoke tests) passed.

✅ Pre-merge checklist

• [x] PR passed smoke test check.
• [x] Feature branch has been rebased against changes from parent branch, as needed
• [x] Resolved all merge conflicts on branch
• [ ] Notified merge coordinator that PR is ready for merge via comment mention

✅ Post-merge checklist

• [ ] Feature branch deleted after merge to clean up repository.
• [ ] Verified that all checks pass on parent branch (e.g., main or release-name) after merge.