In that build I install catch explicitly in the before_install, but I have other tests that I install it in the apt packages section of the yml. Neither seem to be working.
I am running Ubuntu 18 on my local machine and was able to install catch with the command in the before_install and have it working.
The package catch puts that file in /usr/include/catch.hpp. I don’t know how your local machine is finding it as catch/catch.hpp, but something seems amiss.