fix: Add type checking on condition for mypy-boto3

[hnnasit]

Which issue(s) does this change fix?

#5566

Why is this change necessary?

mypy_boto3_lambda which is used for type checking purposes breaks the command. boto3-stubs is a dev dependency and not included in the prod dependencies.

How does it address the issue?

Adds a condition to only import this for type checking.

What side effects does this change have?

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

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

[hawflau]

why don't we just move the boto3-stub requirement to base.txt?
My reason is adding typing for boto3 objects is a good practice and we should extend this to entire SAM CLI code base gradually. However, using conditional imports for typing seems to require lots of effort and hard to test. Moving boto3-stub to base.txt as a prod requirement seems more sustainable and maintainable.

[hnnasit]

Yeah, we could add this to base.txt.

[hnnasit]

There are some issues with updating the reproducible files after adding the dependency to base.txt due to the pyyaml issues. We will address moving the dependency to base.txt in a separate PR to unblock remote invoke regression.