Heroku container registry login

[english-glaswegian]

Running the original main.yml gives the following warning:

Run docker login -u _ -p ${HEROKU_AUTH_TOKEN} registry.heroku.com WARNING! Using -*** the CLI is insecure. Use --password-stdin.

Revised line: run: echo ${HEROKU_AUTH_TOKEN} | docker login -u _ --password-stdin registry.heroku.com

does not produce the warning.