nix: fix incramental flags, again #22

Job	Run time
Check flake validity	27s
Build Exposed Packages (anyrun)	5m 40s
Build Exposed Packages (applications)	1m 51s
Build Exposed Packages (dictionary)	5m 1s
Build Exposed Packages (kidex)	1m 46s
Build Exposed Packages (randr)	2m 1s
Build Exposed Packages (rink)	3m 24s
Build Exposed Packages (shell)	2m 24s
Build Exposed Packages (stdin)	3m 12s
Build Exposed Packages (symbols)	1m 50s
Build Exposed Packages (websearch)	1m 47s
	29m 23s

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