build checks.x86_64-linux.mutation

Reproduce this run
  1. 0.10 s $ /nix/store/vzx1mi9c0xfadmsm9dhd83d005cb1qs9-coreutils-9.8/bin/timeout --kill-after=15s 7200s /nix/store/86n4l5yri6hys3zk2mwy2azcv9prqb8j-nix-2.31.4/bin/nix --extra-experimental-features nix-command --extra-experimental-features flakes --log-format internal-json build --no-link git+https://github.com/NorfairKing/really-safe-money?ref=master&rev=730e87f6197d15fc59bf21c28f1e2c3e4061ce8e#checks.x86_64-linux.mutation --print-build-logs
  2. 0.12 s warning: ignoring untrusted flake configuration setting 'extra-substituters'.
  3. 0.12 s Pass '--accept-flake-config' to trust it
  4. 0.12 s warning: ignoring untrusted flake configuration setting 'extra-trusted-public-keys'.
  5. 0.12 s Pass '--accept-flake-config' to trust it
  6. 2.42 s
  7. 2.50 s Downloading cached really-safe-money-mutation-report from https://cache.staging.nix-ci.com
  8. 2.54 s Progress: 0 of 1 built, 1 of 2 downloaded from cache
  9. 2.54 s Downloading cached really-safe-money from https://cache.staging.nix-ci.com
  10. 2.55 s Progress: 0 of 1 built, 2 of 2 downloaded from cache