these 2 derivations will be built:
  /nix/store/4a4jqi0dfpw1iq99nii8qr40m70bg4wc-test-drv-canary-actual.drv
  /nix/store/idghrarsb0hggxrwfk1p01nmr1c1krl2-test-drv-canary.drv