Merge bitcoin#33558: ci: Use native platform for win-cross task

fa6fd16 ci: Use native platform for win-cross task (MarcoFalke)

Pull request description:

  Forcing the architecture to amd64 is no longer required. Dropping it should have some benefits:

  * Faster CI speed on other arches (riscv64, arm, ...)
  * Unlock the CI task to run on riscv64 at all

ACKs for top commit:
  hebasto:
    ACK fa6fd16, tested on Ubuntu 24.04, RISC-V.

Tree-SHA512: 68a3fc90cc22ab085d6946deb106e50b22e06eebc61523a9dcb53b38a50021a19da26cc29e2cd20f4673ffc5cc10f441dacca7cc799782258351609d9fa04969

Author: fanquake

ci/test/00_setup_env_win64.sh

@@ -8,7 +8,6 @@ export LC_ALL=C.UTF-8
 
 export CONTAINER_NAME=ci_win64
 export CI_IMAGE_NAME_TAG="mirror.gcr.io/ubuntu:24.04"  # Check that https://packages.ubuntu.com/noble/g++-mingw-w64-x86-64-posix (version 13.x, similar to guix) can cross-compile
-export CI_IMAGE_PLATFORM="linux/amd64"
 export HOST=x86_64-w64-mingw32
 export PACKAGES="g++-mingw-w64-x86-64-posix nsis"
 export RUN_UNIT_TESTS=false