fix: ensure correct image property inheritance

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

includes/tests/unit.yml

 .template: &job-test-template
+  image: gitlab.wpdesk.dev:5050/wpdesk/docker-tests/php-box:8.3.2
   tags:
     - unit
   stage: tests
@@ -15,7 +16,6 @@
 
 .template: &job-test-unit-template
   <<: *job-test-template
-  image: gitlab.wpdesk.dev:5050/wpdesk/docker-tests/php-box:8.3.2
   before_script:
     - echo ${WPDESK_CI_VERSION}
     - php --version