Changes

scripts/osmo-ci-docker-rebuild: fix rpi4 failures

It is no longer possible to pull the arm32 image by just using "docker
build --pull". Use a separate pull command with --platform and set an
env var to not use --pull with "docker build".

Related: OS#6627
Related: docker-playground I6e0a84ce7f8357611abc5da856f36d0df247de75
Change-Id: Ibf91bc098f34b43f46680d0395928e60cdd478fc