Refactor AWS system tests to not use @task.branch

[ramitkataria]

After #46584, @task.branch started failing with DownstreamTasksSkipped exception in system tests. So this refactor is to stop those system tests using @task.branch from failing. As a bonus, this also makes the code cleaner!

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[o-nikolas]

There was a change in @task.branch that removed its support from system tests.

Do you have a link to the change?

[ramitkataria]

Yep, here: #46584

[ferruzzi]

That definitely looks like a better way to handle it. I haven't used short_circuit before, can you confirm that it is only short-circuiting the tasks in that task_group and not the entire rest of the dag/test? I wonder how hard it would be (not in this PR, just Some Day:tm:) to add the same run_if, and skip_if options to the task_group decorator.

I'll be traveling the rest of the week; assuming it is confirmed that it only short-circuits the group and not the whole remaining dag, feel free to consider this an approval vote.

[ramitkataria]

Yes, I tested and confirmed that the rest of the dag still runs.
And yea, run_if and skip_if would be nice to have for task groups but I'm also not sure how hard it would be