Since b52808f1ad `cargo` respects the
`$NIX_BUILD_CORES` variable by utilizing `--test-threads`. However, the
`eva` package also parsed the arguments during the test-phase which
caused a failure since `--test-threads` isn't expected by eva's
argparser[1].
Ths fix is in a pending PR[2] that can be applied on top to fix the
build.
[1] https://hydra.nixos.org/build/126069084
[2] https://github.com/NerdyPepper/eva/pull/37
43612e8e1a