Fix GPU addon integ test workflow

[sky333999]

Description of changes

As a follow up to #1965, add the missing ECR login step and also remove the unnecessary step for go test (which is now done as part of the tf apply consistent to our other integ tests).

License

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Tests

Passing GH run: https://github.com/aws/amazon-cloudwatch-agent/actions/runs/21013574773

Requirements

Before commiting your code, please do the following steps.

1. Run make fmt and make fmt-sh
2. Run make lint

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Integration Tests

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[the-mann]

hmm, seems like the passing test run you linked is failing? https://github.com/aws/amazon-cloudwatch-agent/actions/runs/21013574773

[sky333999]

hmm, seems like the passing test run you linked is failing? https://github.com/aws/amazon-cloudwatch-agent/actions/runs/21013574773

I undid the change to point to my branch of the test repo and it made it weird for some reason.

Anyway, created a temp branch and reran here: https://github.com/aws/amazon-cloudwatch-agent/actions/runs/21075018664/job/60614650809