fix(ecs): enableDeploymentAlarms should mutate the alarmNames property

[vito-laurenza-zocdoc]

Issue #36308

Closes #36308

Reason for this change

Fixes a silent bug in the ecs module.

Description of changes

The code is mistakenly using concat() which returns a new array rather than modifying the existing one (which was the original intent of the code).

Describe any new or updated permissions being added

n/a

Description of how you validated changes

test case added

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[aws-cdk-automation]

(This review is outdated)

[github-actions]

	Tests	Passed ❌️	Skipped	Failed
Security Guardian Results	0 ran	0 passed	0 skipped	0 failed

Test	Result
No test annotations available

• View Security Guardian Results

[github-actions]

	Tests	Passed ❌️	Skipped	Failed
Security Guardian Results with resolved templates	0 ran	0 passed	0 skipped	0 failed

Test	Result
No test annotations available

• View Security Guardian Results with resolved templates

[pahud]

This PR is currently blocked by this:

❌ Fixes must contain a change to an integration test file and the resulting snapshot.

You will need to add/update integ test to unblock this or if you think integ tests are not necessary, please follow the suggestion #36309 (review)

[vito-laurenza-zocdoc]

This PR is currently blocked by this:

❌ Fixes must contain a change to an integration test file and the resulting snapshot.

You will need to add/update integ test to unblock this or if you think integ tests are not necessary, please follow the suggestion #36309 (review)

Thanks. I've added basic coverage for this case in the existing integration test as it was not exercised there before.

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.