Nixify shellcheck

Add shellcheck command to flake.nix and use it in the Gitlab

flake.nix

@@ -39,6 +39,10 @@
 					package = self'.packages.cache;
 					category = "utils";
 					help = "Downloads ISO files and adds them to the S3 bucket";
+				} {
+					package = self'.packages.shellcheck;
+					category = "utils";
+					help = "Run shellchecks";
 				} ];
 			};
 
@@ -62,6 +66,20 @@
 					];
 					text = builtins.readFile ./cache-restore.sh;
 				};
+				shellcheck = pkgs.writeShellApplication {
+					name = "shellcheck";
+					runtimeInputs = with pkgs; [
+						shellcheck
+					];
+					text = ''
+						scripts=()
+						shopt -s globstar
+						for f in **/*.sh; do
+							scripts+=("$f")
+						done
+						shellcheck -e SC2239 "''${scripts[@]}"
+					'';
+				};
 			};
 
 			# https://numtide.github.io/treefmt/