west.yml: MCUboot synchronization from upstream

Update Zephyr fork of MCUboot to revision:
  5d6471bac184c8accaeeb0efcfad8dd35225a28d

Brings following Zephyr relevant fixes:
  - 5d6471ba zephyr: convert platform_allow to a list
  - 7cc60059 boot: zephyr: boards: nrf54l10 and nrf54l05 configs
  - 742978e7 boot: zephyr: Fix
    sample.bootloader.mcuboot.usb_cdc_acm_recovery
  - 39aab3d8 zephyr: Add CONFIG_MCUBOOT_CLEANUP_RAM

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>