fix: Add type hints for iam api-client samples

[glasnt]

Description

Fixes b/280879750

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• Tests pass: nox -s py-3.9 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[rsamborski]

Thanks, approved.
Future ask: please remember to add a link to the bug in the PR description for reference (I've added it myself this time).

[kweinmeister]

LGTM. Just curious, there are several # type: ignore comments added. These are impractical to address?

[glasnt]

The # type: ignore were to convince mypy not to inspect the types of the imports. Fixit guidance said to use mypy, but CI uses flake8-annotations instead. I'm happy to remove these.

[rsamborski]

@kweinmeister wrote:

LGTM. Just curious, there are several # type: ignore comments added. These are impractical to address?

@glasnt followed official guidance (see here), so I think we should leave as is.