refactor: use own images instead of composer

Signed-off-by: Bart Jaskulski <bjaskulski@protonmail.com>

includes/prepare.yml

 prepare prefixed vendor:
-  image: composer:2.0.8
+  image: gitlab.wpdesk.dev:5050/wpdesk/docker-tests/php-box:7.4
   artifacts:
     name: "vendor_prefixed"
     paths:
@@ -47,7 +47,7 @@ prepare npm assets:
     - if [[ -f tests/codeception/prepare_npm.sh ]]; then sh tests/codeception/prepare_npm.sh; fi
 
 prepare translations:
-  image: composer:2.0
+  image: gitlab.wpdesk.dev:5050/wpdesk/docker-tests/php-box:7.4
   artifacts:
     name: "language"
     paths: