fix: Cypress test creating an Image without a `cy-test` prefixed label

[bnussman-akamai]

Description 📝

• I made a mistake in https://github.com/linode/manager/pull/10471 (specifically here)
• I removed the randomLabel() from the createImage call because at the time, it didn't occur to me that the image label mattered for the sake of the test. I was correct in that sense, but I failed to remember that cypress only cleans up entities that are prefixed with cy-test 🤦 . Our test accounts are filling up with Images that are not being cleaned up as a result 😣
• This PR adds back the randomLabel() so the image is created with a label that will be cleaned up

How to test 🧪

• Verify the image created by create-stackscripts.spec.ts are prefixed with cy-test

As an Author I have considered 🤔

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• [ ] ➕ 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
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[github-actions[bot]]

Coverage Report: ✅
Base Coverage: 81.64%
Current Coverage: 81.64%