If you are facing this issue and are unable to upgrade to the fixed version of curl, you can install it temporarily to get upgrades working again:
$ sudo rpm-ostree usroverlay
$ curl -LO https://kojipkgs.fedoraproject.org//packages/curl/7.65.3/1.fc30/x86_64/curl-7.65.3-1.fc30.x86_64.rpm
$ sudo rpm -ihv curl-7.65.3-1.fc30.x86_64.rpm
$ sudo systemctl restart rpm-ostreed
And then retry rpm-ostree upgrade
Once you reboot, the temporary usroverlay is discarded and you’ll be in the latest deployment with the fixed version of curl