Deprecation warning on GitHub actions: node12, save-state, and set-output

[tompollard]

It looks like we may need to make some changes to our GitHub Actions workflow at some point. See: https://github.com/MIT-LCP/physionet-build/actions/runs/6343761694?pr=2086

The following actions uses node12 which is deprecated and will be forced to run on node16: docker/setup-buildx-action@v1, docker/build-push-action@v2. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

The save-state command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

The set-output command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/