Failing Git over HTTPS since certificate upgrade

Important background: Today (morning of March 1, 2023), we switched to a new X.509 (SSL/TLS) certificate for HTTPS, issued by "GEANT Vereniging", "GEANT OV RSA CA 4".

On my Ubuntu 20.04.5 LTS., any git operation clone, push, pull over HTTPS are failing:

$ git pull origin main
fatal: unable to access 'https://gitlab.ub.uni-giessen.de/some/project.git/': server certificate verification failed. CAfile: none CRLfile: none

Access via Firefox browser works fine.

I suspect that some part of my system needs to know about the root certificate of the new certificate..?

Edited Mar 01, 2023 by Johannes Keyser