allow unset variables in nix-build-and-cache for unset ATTIC_TOKEN

Signed-off-by: strawberry <strawberry@puppygock.gay>

bin/nix-build-and-cache

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-set -euo pipefail
+set -eo pipefail
 
 # The first argument must be the desired installable
 INSTALLABLE="$1"