Add tini to container to fix build

[tomtrafford]

After make zpkg commands fail after Synthesis I found this post on stack overflow:
https://stackoverflow.com/questions/55733058/vivado-synthesis-hangs-in-docker-container-spawned-by-jenkins

which seemed to match the problem we have been encountering. When run in docker there is no PID 1 process which automatically cleans up zombie processes. This adds tini to the CI container which will clean up zombie processes.

I have found adding this to the container and running the make zpkg command with tini running as a process subreaper fixes the problem.

[coretl]

Would adding --init to this line instead work?
https://github.com/PandABlocks/PandABlocks-FPGA/blob/d4e8f308f4a684c5d5805ad0d04a3ccc4f8a6d57/.github/workflows/_make_zpkg.yml#L26

This is suggested at the end of https://stackoverflow.com/a/60614779

[tomtrafford]

I tried adding the --init flag there but it didn't seem to fix the problem. I will run another test job on the FPGA repo to see what it changes.

[tomtrafford]

When passing '--init' or without I find that there is another proccess running with PID 1:

2025-01-06T13:09:16.8087839Z     PID TTY          TIME CMD
2025-01-06T13:09:16.8088270Z       1 ?        00:00:00 tail

When I use tini I found that this process interfered with it and it wouldn't run with PID 1. I therefore had to pass the -s argument with tini around the 'make zpkg' command. This registers Tini as a process subreaper for that process, without it running on PID 1.

I don't know where the tail process is coming from. Locally I get this within the container:

    PID TTY          TIME CMD
      1 pts/0    00:00:00 bash

[coretl]

I don't know where the tail process is coming from. Locally I get this within the container:

https://github.com/orgs/community/discussions/41644

When passing '--init' or without I find that there is another proccess running with PID 1:

I guess that makes sense if GitHub actions always wants to run tail as PID 1 to keep the container alive. Your solution is probably the only one that will work then, unless @gilesknap has any ideas