test: [M3-8864] - Cypress tests to validate errors in Linode Create Backups tab

[pmakode-akamai]

Description 📝

Add Cypress test to validate error messages if required options are not selected in the Linode Create Backups tab.

• Related to: change: [M3-8461] - Improve validation error when a backup is not selected. #11147

Changes 🔄

List any change(s) relevant to the reviewer.

• Add a Cypress test to validate error messages if required options are not selected in the Linode Create Backups tab.

Target release date 🗓️

N/A

How to test 🧪

• yarn cy:run -s "cypress/e2e/core/linodes/create-linode.spec.ts"
• Ensure all tests pass

Author Checklists

As an Author, to speed up the review process, I considered 🤔

👀 Doing a self review
❔ Our contribution guidelines
🤏 Splitting feature into small PRs
➕ Adding a changeset
🧪 Providing/improving test coverage
🔐 Removing all sensitive information from the code and PR description
🚩 Using a feature flag to protect the release
👣 Providing comprehensive reproduction steps
📑 Providing or updating our documentation
🕛 Scheduling a pair reviewing session
📱 Providing mobile support
♿ Providing accessibility support

• I have read and considered all applicable items listed above.

As an Author, before moving this PR from Draft to Open, I confirmed ✅

• All unit tests are passing
• TypeScript compilation succeeded without errors
• Code passes all linting rules

[linode-gh-bot]

Cloud Manager UI test results

🎉 467 passing tests on test run #3 ↗︎

❌ Failing	✅ Passing	↪️ Skipped	🕐 Duration
0 Failing	467 Passing	2 Skipped	91m 18s

[mjac0bs]

Confirmed the test passes and provides coverage for error validation in the original ticket. Thanks!

[dwiley-akamai]

Test passes locally & in CI ✅