Fix mypy type errors in DynamoDB example system test

[23tae]

This PR resolves the mypy [arg-type] error in the DynamoDB example system test.

Description

The type error occurred because task variables (create_table, delete_table) shadowed the helper function names. This confused mypy's type inference when passing these variables to chain().

Key changes

• Renamed the shadowed task variables to create_table_task and delete_table_task.
• Removed the obsolete # TODO: FIXME and # mypy: disable-error-code="arg-type" comments.

Verification Results

I have verified the changes locally:

• Static Checks (Prek): Passed
• Unit Tests (Breeze): Passed

---

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[vincbeck]

Seems to not be working

[23tae]

Seems to not be working

Rebased on main to pull in #68857, which fixes the unrelated mypy error in login.py. The mypy checks are passing cleanly now.
@vincbeck Just to clarify, was your comment regarding the CI failures, or is something else not working?