In resource-constrained environments such as CI, we may hit this new
limit, which prevents deployments from succeeding.
Following the lead of the ironic devstack plugin, we reduce the limit to
256MB.
Depends-On: https://review.opendev.org/c/openstack/kayobe/+/777518
Change-Id: I2d853d38740dca445cd281b83f4a26d842a9c9cd