Enable the airflow.utils.timezone ban rule

[FrankYang0529]

Why

• Set up process for sharing code between different components. #53149 added a ruff banned-api entry for airflow.utils.timezone but left it commented out behind # Add this once providers are sorted.
• Use common.compat.sdk for timezone imports in providers #70492 and Use common.compat.sdk for the remaining provider timezone imports #71209 cleared the provider call sites, so we can enable the rule.

How

• devel-common keeps its Airflow 2 fallbacks.
• Uncomment the rule and drop the # Add this once providers are sorted note it was waiting on.

---

Was generative AI tooling used to co-author this PR?

• Yes - Claude Code

---

• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst, in airflow-core/newsfragments. You can add this file in a follow-up commit after the PR is created so you know the PR number.

[Lee-W]

why the noqa