osu-lazer-bin: set `OSU_EXTERNAL_UPDATE_PROVIDER` to ensure that Velo… #779

Job	Run time
check (nix run nixpkgs#alejandra -- -c . -e ./npins) / nix	43s
check (NIXPKGS_ALLOW_INSECURE=1 nix flake check --accept-flake-config --impure) / nix	3m 12s
build / build (faf-client) / nix	53s
build / build (faf-client-unstable) / nix	1m 3s
build / build (proton-ge) / nix	28s
build / build (umu) / nix	42s
build / build (wine-osu) / nix	1m 0s
build / build (wine-ge) / nix	1m 18s
build / build (wine-tkg) / nix	1m 18s
	10m 37s

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