Exclude generated non-RefCounted objects from the tests

[aaronfranke]

This PR excludes functions from the regression test project when both of these are true:

• The function returns a non-RefCounted Object type, such as Node-derived classes.
• The function name contains the word "generate".

The intention here is to exclude objects that are intentionally owned by the function caller, otherwise the regression test project step reports calls to those functions as memory leaks when Godot exits.

Example of a failing CI run: https://github.com/godot-dimensions/godot/actions/runs/33378365263/job/99444996137

Example of a passing CI run, where the only change compared to the failing run is pointing the CI at this branch: https://github.com/godot-dimensions/godot/actions/runs/33413334316/job/99561138386

[qarmin]

ubuntu-20.04 ci image needs to be updated to fix freezes in CI