Add /tmp to container

[dmikusa]

Summary

The Dockerfile for the actions was not adding '/tmp', it can't because it's a scratch image and there's no shell. Github Actions don't create /tmp either so there's no temp directory.

The Github runner temp directory does not help either because that's a path on the VM not in the container where the action runs.

As such, we are making /tmp in code and then using /tmp specifically for tempfiles.

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).