To update syncthing, it has proven useful to update the tarball URL and hash and then
- comment generated-sources.json in syncthing.yaml
- enable network for the build, i.e. uncomment the build-args
- run flatpak-builder, e.g. flatpak-builder --user --ccache --keep-build-dirs --force-clean -v --repo=/tmp/fb.repo fpbuilder net.syncthing.syncthing.yaml
- run the go-vendor generator, e.g. python3 ~/vcs/flatpak-builder-tools/go-get/flatpak-go-vendor-generator.py .flatpak-builder/build//syncthing/vendor/modules.txt > go-sources.json
- undo a) and b)