CI: Windows: Use separate config file for Docker
Rather than relying on global state for 'docker login' credentials, use a local file so we don't collide with other simultaneous builds.
[cherry-picked from mesa/mesa!6446 (merged)]
Rather than relying on global state for 'docker login' credentials, use a local file so we don't collide with other simultaneous builds.
[cherry-picked from mesa/mesa!6446 (merged)]