Fix props mutation in anomaly.vue

What does this MR do?

Upgrade to @vue/test-utils 1.x revealed props mutation in anomaly.vue resulting in infinite render loop in tests.

Fix this behavior by using immer to properly generate derived value and avoid props mutation

Screenshots (strongly suggested)

N/A

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done