Update GB committee membership and chairs

[HarHarLinks]

Description

🎩 Vice Chair of the Governing Board

This can be merged no earlier than 2025-12-05.

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[HarHarLinks]

tbd:

• remove Robin from MD role
• determine whether Amandine moves into (acting) MD role, stays in Guardian role, or both (https://matrix.org/media/2025-04-governing-board-terms-of-reference.pdf 2.1 and 2.4.1)