Fix staging deploy github action

[xmunoz]

I rule and have completed some work on Case Manager that's ready for review!

Staging is no longer being autodeployed from main. This is the error message:

/bin/sh: 1: heroku: not found
Created and wrote to ~/.netrc
Successfully logged into heroku
/bin/sh: 1: heroku: not found

This is because heroku no longer comes packaged with the default image of the ubuntu-latest Github-hosted runner (24.04). It was pre-installed on 22.04 however, hence the breakage. They claim to have removed it for "maintenance reasons" 🙄

This PR explicitly installs heroku cli in the staging deploy workflow, and updates the heroku-deploy Github Action to the latest version.

https://devcenter.heroku.com/articles/heroku-cli

[xmunoz]

Successful workflow run: https://github.com/DARIAEngineering/dcaf_case_management/actions/runs/11187413238/job/31104408138

[lomky]

🎉