Run deployments only on original repository

I made a fork of the repository. It tried to deploy to staging but failed because I don't have the right credentials. However, the CI shouldn't completely fail on forks, it should be skipped if possible.

Start by locating the CI deployment configuration and inspect how staging deployments are triggered for forks. Done means forked repositories skip deployment without making the CI run fail, while the original repository can still deploy to staging.

Written by the indexing model from the issue text.