Updates to AWS ECS deploy guide

[thekaveman]

Why:

Following the steps in the guide, errors will occur running the workflow due to these syntax problems.

• Example failed run with the guide syntax for environment variables before these changes: https://github.com/cal-itp/docker-django-aws-test/actions/runs/494684748

• Example successful run with the updated environment variable syntax reflected in this PR: https://github.com/cal-itp/docker-django-aws-test/actions/runs/494699023

• Example failed run with the output redirect to $GITHUB_ENV before these changes: https://github.com/cal-itp/docker-django-aws-test/runs/1724635263

• Example successful (step) with the updated ::set-ouput syntax reflected in this PR: https://github.com/cal-itp/docker-django-aws-test/runs/1724692920

What's being changed:

• Syntax of environment variables used in jobs.<job_id>.steps[*].with, from $ENV_VAR to ${{ env.ENV_VAR }}
• Fix to output command, from redirecting to $GITHUB_ENV to using ::set-output name=variable::

Check off the following:

• I have reviewed my changes in staging. (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

Direct link to staging deploy: https://docs-3002--aws-ecs-updates.herokuapp.com/en/actions/guides/deploying-to-amazon-elastic-container-service

[welcome]

Thanks for opening this pull request! A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.

[janiceilene]

@thekaveman Thanks so much for opening a PR! I'll get this triaged for review ✨

[github-actions]

This PR is stale because it has been open 7 days with no activity and will be automatically closed in 3 days. To keep this PR open, update the PR by adding a comment or pushing a commit.

[thekaveman]

Please don't close!

[lucascosti]

Thanks so much for these fixes, @thekaveman! And also thanks for the awesome explanation and links to your workflow runs! 🙇‍♂️

I'll get this merged in 🚀

[github-actions]

Thanks very much for contributing! Your pull request has been merged 🎉 You should see your changes appear on the site in approximately 24 hours.