Update `SmokeTestDecoratorTest` (#3840)

## Motivation and Context
<!--- Why is this change required? What problem does it solve? -->
<!--- If it fixes an open issue, please link to the issue here -->
Add tests the were skipped in
https://github.com/smithy-lang/smithy-rs/pull/3836

 in favor of merging
and unblocking customer.

## Description
<!--- Describe your changes in detail -->
Testing our smoketest generator with the `UseDualStack` and `UseFips`
endpoint built-ins. Previously the smoketest generator assumed that
these were always available, but they are only available if those
built-ins are included in the endpoints rule set of the model. We now
test the smoke test with both of these built-ins, with each by itself,
and with neither.

## Testing
<!--- Please describe in detail how you tested your changes -->
<!--- Include details of your testing environment, and the tests you ran
to -->
<!--- see how your change affects other areas of the code, etc. -->


## Checklist
Just a test change, no changelog

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Co-authored-by: ysaito1001 <awsaito@amazon.com>