ci: add basic integration test for pmb

Yes, I know this is crude/basic, but others are welcome to improve it later. I think we need some integration testing asap, and this is better than nothing :D

.gitlab-ci.yml

@@ -23,7 +23,7 @@ integration:
   before_script:
     - *global_before_scripts
     - apk upgrade -U
-    - apk add python3 git openssl doas
+    - apk add doas git losetup python3 openssl
     - echo "permit nopass build" > /etc/doas.d/ci-user.conf
   script:
     - ".ci/integration.sh"