chore: use nix-hash --to-base16 not nix --to-base16
This fixes new errors of the form:
```
warning: 'to-base16' is a deprecated alias for 'hash to-base16'
error: experimental Nix feature 'nix-command' is disabled; use '--extra-experimental-features nix-command' to override
```
Example failed build:
@@ -23,7 +23,7 @@ read_sha256_from_nix_sources() {
SHA256_BASE32=$(jq -r .'"'"$KEY"'".sha256' "$NIX_SOURCES_JSON")
- nix to-base16 --type sha256 "$SHA256_BASE32"
+ nix-hash --to-base16 --type sha256 "$SHA256_BASE32"
}
read_url_from_nix_sources() {
