You can't signup on Gitlab with a throwaway email service, even Github allows you to do that (even though they flag the account soon but with a simple message they re-activate it). Generally whether a service accepts a throwaway mail for signup is a good indication of how tolerant it is.
art wrote
You can always spin up a server running Gitea and have your own private git server. notabug.org uses Gogs and Gitea is a more modern fork.