ci: updated the rules to only run on changes to a subset of files

.gitlab-ci.yml

@@ -45,6 +45,13 @@ build:
     - git pull origin main
   script:
     - nix --experimental-features 'nix-command flakes' run nixpkgs#colmena -- build
+  only:
+    changes:
+      - applications/**/*
+      - machines/**/*
+      - secrets/**/*
+      - flake.*
+      - .gitlab-ci.yml
 
 # every commit on main will build and deploy
 deploy:
@@ -65,4 +72,10 @@ deploy:
     - nix --experimental-features 'nix-command flakes' run nixpkgs#colmena -- apply --on @active
   only:
     refs:
-      - main
+      - main
+    changes:
+      - applications/**/*
+      - machines/**/*
+      - secrets/**/*
+      - flake.*
+      - .gitlab-ci.yml