modif: use nix inside gitlab-ci

.gitlab-ci.yml

 ---
+variables:
+  NIX_PATH: nixpkgs=channel:nixos-unstable
 
 stages:
   - lint
@@ -6,13 +8,13 @@ stages:
 ansible:
   stage: lint
   needs: []
-  image: registry.cri.epita.fr/cri/docker/ansible/master
+  image: registry.cri.epita.fr/cri/infrastructure/nixpie/nix
   script:
-    - ansible-lint
+    - nix-shell -p ansible-lint --run ansible-lint
 
 yaml:
   stage: lint
   needs: []
-  image: registry.cri.epita.fr/cri/docker/ansible/master
+  image: registry.cri.epita.fr/cri/infrastructure/nixpie/nix
   script:
-    - yamllint -f colored .
+    - nix-shell -p yamllint --run 'yamllint -f colored .'