We can’t migrate from Trusty to Xenial or Bionic because our (radare2 disassembler and debugger) tests require running debugging tests (to test debugging features obviously) that often require PTRACE. Older environments (Trusty) allowed this. But switching to anything newer doesn’t work, neither with sudo: required nor with sudo: true. Any recommendations how to enable them?
Long story short, in Trusty, Docker’s default seccomp profile is not enabled as it should – that’s why it happens to work. In later distributions where that’s fixed, you need to explicitly give the container any additional privileges that it requires.
Travis has a stock Docker installed (I don’t know from which package in particular but that can be checked), so any “answer specific to Docker in general” should apply.
Unless you can somehow show that it doesn’t and the problem is at Travis side rather than with your project, the argument is over nothing.