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.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6446>
1 file changed