e2e tests: Fix E2E selectors for WordPress trunk list tables

[priethor]

What

Update the E2E row-checkbox selectors to work with both the <th> markup used by released WordPress versions and the <td> markup now used by WordPress trunk.

Why

WordPress Core changed list-table checkbox cells from <th> to <td> in ae5d691. The existing element-specific selector no longer finds those checkboxes on trunk, which breaks cleanup and allows retries to accumulate duplicate records.

Testing Instructions

• git diff --check
• npx wp-scripts lint-js tests/e2e/import-export.spec.ts tests/e2e/options-page-admin.spec.ts tests/e2e/post-type-admin.spec.ts
• E2E tests were not run locally.

Use of AI Tools

I used OpenAI Codex to update the selectors. I reviewed the diff and test results.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props priethor.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.