Others have run into this too – the general advice is that upping the number of open files allowed with ulimit tooling is the only real option. I did find a related thread though that indicated usually this is caused by another process on the same machine, not promtail itself. In other words, promtail here may be the victim not the culprit.
Given that you’re running docker compose, you might want to check your host OS and how it’s doing, just as a thought. Your options boil down to increasing the limit with ulimit or terminating some other fd-hungry process.