Upgrading puma to version 6 solves deployment issues in Render

[heratyian]

any more details @rsfarzo ?

It's been an off and on issue, and my first experience with it was around January in one of my own apps.

Some student apps deploy fine with puma 5. I've experimented with removing any major version, and that's worked.

An additional side-issue was in omnicalc-1, where there was an error like not finding activesupport/all

And commenting out #require "activesupport/all" in environment.rb solved that.