GitHub Action Flatpak build fails by running out of diskspace

[blissd]

The GHA builds for Fotema are failing with an error that looks like the build is using all the diskspace. I've had a go using some methods for "reclaiming" diskspace in the GHA builds, but they had no effect.

As far as I can tell, GHA runners have 14GB of usable diskspace. Looking at the build directory on my dev laptop, I see Fotema is using about 17GB... which sounds like a lot to me.

I'd really like the GHA Flatpak build to work, either by somehow freeing up more diskspace, or by modifying the build to use less diskspace.