fix(report): use nix eval to list the components

This is less error prone than parsing the information from `nix flake
show`.

scripts/create-report.sh

@@ -11,7 +11,7 @@ system=$(nix eval --impure --json --expr 'builtins.currentSystem')
 
 # Extract the names of a flake attrset
 get_names() {
-  nix eval --json --apply builtins.attrNames "$1"
+  nix eval --json --apply builtins.attrNames "$1" 2>/dev/null || echo '[]'
 }
 
 group "Show Packages for $system"