Fix sysbuild

https://git.m-labs.hk/M-Labs/nix-scripts/commit/596f4cf4b9832e90c8f4e5fb07c5e8046126d3ca

Created by  Eelco Dolstra  on October 22, 2020
IPBPZCWRYRDDX4YK3Z4JYXNOI77RYN2ARKMYV2U37RVBP5I7D6BQC
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