How can I get the debug extension for a test build?

I have a segfault in the test build for flathub-beta with the new 22.08 freedesktop runtime, so I’d like to debug it. The buildbot tells me where I can find the flatpakref for the build, but how do I get the corresponding .Debug package? (I tried inserting .Debug before .flatpakref in the URL, but that gives a 404, while the directory gives a 403)