Without this, the plugin cannot be loaded in a devenv because the RPATH is not added to the plugin dylib. This RPATH will be stripped on install, which is what we want. When deploying apps, people are supposed to use `macdeployqt` to create an AppBundle that bundles Qt for you and sets the RPATHs correctly to point to that bundled Qt. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3708>