The GPL contract only says you have to distribute source to the users you give binaries to. The only people who can ask for said source are the people receiving those binaries and the only people who have standing to sue when that doesn’t happen is the copyright owners.
That’s why you can use GPL software in your private CI system and not need to give anyone the source code.
That’s why you can use GPL software in your private CI system and not need to give anyone the source code.