[Whitelisted Caller] Runtime Upgrade to v1.6.2

This is a referendum that authorises the upgrade of the Polkadot Relay Chain to version 1.6.2. This version includes an urgent relay chain fix for the bug that has caused the Kusama stall.

If approved, the authorisation will be enacted at block #27705996, estimated time: 2025-09-10 08:45:39 (UTC).

For the full list of changes, please read the fellowship 1.6.2 release notes.

It is important that this runtime upgrade is enacted before #1721 which enables RFC103. For that reason I temporarily removed the #1721 pre-image.

Whitelist: https://collectives.subsquare.io/fellowship/referenda/394