flake: limit to 64-bit linux

12 jobs for master in 26 seconds (queued for 2 seconds)
Name Stage Failure
polkadot-spec Fetch
$ cachix use w3fpkgs
Configured https://w3fpkgs.cachix.org binary cache in /etc/nix/nix.conf
$ nix eval .#${CI_JOB_NAME}.outPath | cachix push w3fpkgs
warning: Git tree '/builds/florian/w3fpkgs' is dirty
error: --- Error --- nix
flake 'git+file:///builds/florian/w3fpkgs?shallow=1' does not provide attribute 'packages.x86_64-linux.polkadot-spec.outPath', 'legacyPackages.x86_64-linux.polkadot-spec.outPath' or 'polkadot-spec.outPath'
All done.
Cleaning up file based variables
ERROR: Job failed: command terminated with exit code 1