Fix broken RST link in New PMC Member Onboarding steps

[coleheflin]

Fix malformed RST hyperlink syntax in the New PMC Member Onboarding section of COMMITTERS.rst.

The link was written as:

`<PMC Responsibilities>https://community.apache.org/pmc/responsibilities.html`_

Which is invalid RST — the display text and URL were swapped. Corrected to:

`PMC Responsibilities <https://community.apache.org/pmc/responsibilities.html>`_

---

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

• Yes — Claude Sonnet 4.6

Generated-by: Claude Sonnet 4.6 following the guidelines

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide (https://github.com/apache/airflow/blob/main/contributing-docs/README.rst)
Here are some useful points:

• Pay attention to the quality of your code (ruff, mypy and type annotations). Our prek-hooks will help you with that.
• In case of a new feature add useful documentation (in docstrings or in docs/ directory). Adding a new operator? Check this short guide Consider adding an example DAG that shows how users should use it.
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[jason810496]

TY!

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.