Reenable podio tests in edm4hep workflows

[tmadlener]

    I have disabled the podio tests in the edm4hep workflows for the moment, because using `PODIO_SET_RPATH` does not seem to work in downstream edm4hep in this environment, even when also using `RPATH` to build there. I will open an issue to keep track of that, but in order to unblock this, I figured disabling the podio tests (which are run in any case in other workflows) is the easiest way forward.

Originally posted by @tmadlener in #333 (comment)

The main reason for this is that discovering the individual test cases from Catch2 runs an executable, which picks up the podio from the underlying system on ubuntu. This would be fixable by using RPATH during the build process, but that then breaks the edm4hep tests.

[tmadlener]

Given the large overlap between the stacks that we use for the edm4hep CI workflows and the ones that we use for building regular podio, there is no real benefit any longer from also running the podio tests for the workflows where we build and test EDM4hep. I am closing this.