display the command that was used to generate the failure

Would it be possible to display the relevant command (documented in the README at https://github.com/NixOS/ofborg) that generated the error.
For instance, instead of

error: while evaluating anonymous function at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/.gc-of-borg-outpaths.nix:39:12, called from undefined position:
while evaluating anonymous function at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/pkgs/top-level/release-lib.nix:121:6, called from /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/lib/attrsets.nix:292:43:
while evaluating 'hydraJob' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/lib/customisation.nix:157:14, called from /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/pkgs/top-level/release-lib.nix:121:14:
while evaluating the attribute 'drvPath' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/lib/customisation.nix:174:13:
while evaluating the attribute 'drvPath' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/lib/customisation.nix:141:13:
while evaluating the attribute 'configurePhase' of the derivation 'lua5.1-luaevent-0.4.4-1' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/pkgs/development/interpreters/lua-5/build-lua-package.nix:92:3:
undefined variable 'libevent' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/pkgs/development/lua-modules/overrides.nix:52:25

get sthg like (not sure it's correct though):

$ curl -o outpaths.nix https://raw.githubusercontent.com/NixOS/ofborg/released/ofborg/src/outpaths.nix
$ GC_INITIAL_HEAP_SIZE=4g nix-env -f ./outpaths.nix -qaP --no-name --out-path --arg checkMeta true > out-paths
error: while evaluating anonymous function at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/.gc-of-borg-outpaths.nix:39:12, called from undefined position:
while evaluating anonymous function at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/pkgs/top-level/release-lib.nix:121:6, called from /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/lib/attrsets.nix:292:43:
while evaluating 'hydraJob' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/lib/customisation.nix:157:14, called from /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/pkgs/top-level/release-lib.nix:121:14:
while evaluating the attribute 'drvPath' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/lib/customisation.nix:174:13:
while evaluating the attribute 'drvPath' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/lib/customisation.nix:141:13:
while evaluating the attribute 'configurePhase' of the derivation 'lua5.1-luaevent-0.4.4-1' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/pkgs/development/interpreters/lua-5/build-lua-package.nix:92:3:
undefined variable 'libevent' at /var/lib/ofborg/checkout/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/eval-1-lassulus.ewr1.nix.ci/pkgs/development/lua-modules/overrides.nix:52:25

It would help comitters run the tests locally

Start with the command documented in the README and the outpaths.nix example shown in the issue, then locate where ofborg formats evaluation failures. Done means the relevant command is included with the displayed error so committers can reproduce the failure locally.