CircleCI: update BUILDX_VERSION to v0.6.0
CircleCI: update BUILDX_VERSION to v0.6.0

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

thaJeztah/cli,cpuguy83/cli,thaJeztah/cli,docker/cli,docker/cli,cpuguy83/cli