Since I started to do my personal projects, I figured out that storing the answers for might current doubts might be very useful later, when I have the same issues again. Sometimes I stuggle to find the answer I know I've found before. This gist will help with that and will be refered back on the projects that needs it!
When you start a new project with Heroku, the default stack might be the buildpack according to the files your repository have. Usually in my projects I like to use the Container Stack, so I can build the Dockerfile myself, that gives me control on the environment my application is working on. So, in order to fix that, I neet to run the command to change the default stack.
$ heroku stack:set container -a <app-name>