Update GitLab CI Docker push job

[yhao3]

Description

This pull request includes the following changes:

1. Remove the unnecessary REGISTRY_URL variable, as the predefined CI_REGISTRY can be used instead.
2. Update the Docker push configuration to use the predefined CI_REGISTRY_USER and CI_REGISTRY_PASSWORD variables instead of "gitlab-ci-token" and CI_BUILD_TOKEN.
3. Update comments to reflect changes and improve clarity.

[mraible]

It looks like you need to run npm run update-snapshots.

[yhao3]

Hi @mraible,

Thanks for the reminder! I’ve run npm run update-snapshots, and the CI build is now passing. Please let me know if there’s anything else I need to address.