test: [M3-6221] - Clean up cy.intercept calls in support ticket create test

[jdamore-linode]

Description 📝

Quick clean up to replace calls to cy.intercept with utils in our support ticket create test.

Changes 🔄

• Replace calls to cy.intercept with mock utils in open-support-ticket.spec.ts.
• Adds mockAttachSupportTicketFile() util

How to test 🧪

We can rely on CI to confirm that this test has not been broken by these changes, but to run the test locally you can use this command:

yarn cy:run -s "cypress/e2e/core/helpAndSupport/open-support-ticket.spec.ts"

As an Author I have considered 🤔

Check all that apply

• 👀 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

[github-actions]

Coverage Report: ✅
Base Coverage: 82.01%
Current Coverage: 82.01%

[abailly-akamai]

🚢

Code looks good ✅
Both tests passing as expected ✅