Expose ports on github-hosted runner


is it possible to expose a service running on a git-hub hosted runner to the internet?

One of my projects contains a very simple acme-client. I would like to validate the functionality by connecting to the LetsEncrypt Staging environment and enroll a certificate from there. As part of the http-challenge validation LE needs to establish a connection to port 80 to the runner executing the workflow. I am already able to get the public ip-address of this runner and can modify my respective DNS entries. However, it seems that the port 80 of my client-application is not accessible from outside.

Any idea if this is possible? Or do I need to use a self-hosted runner to get this done?

Thank you for your help and have a nice day