fix(iam): fix tests in cloud-client/snippets

[eapl-gemugami]

Description

Fixes Internal: b/392857134

• Solves errors on nox -s py-3.8 and nox -s py-3.12, by adding an exponential backoff.
• Updates dependencies to latest version.
• Fixes linting errors and suggestions.
• Unifies Style across all the snippets folder.

Follow-up of #13010

Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• Tests pass: nox -s py-3.12 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• Please merge this PR for me once it is approved

[ghost]

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[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• iam/cloud-client/snippets/create_deny_policy.py:20, tag iam_create_deny_policy

You are about to delete 1 region tag.

• iam/cloud-client/snippets/create_deny_policy.py:17, tag iam_create_deny_policy

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