After not pushing anything for 10 months, new GitHub pushes won’t trigger builds on Travis anymore.
I can trigger new builds manually, which will work (but only for branches, tags cannot be triggered manually).
10 months before, builds were triggered just fine, and I have not changed anything since then.
Just disable the project on Travis, as described above. Then on GitHub, go through the project settings and remove or disable everything that has Travis’ name in it. Especially the Travis webhook. Then, re-enable the project on Travis.
In case you are asking yourself if you also need to remove the Travis permissions on the organization/user level – no need for that. Only concern yourself with the GitHub project settings, not with the level above.