Attempting to fix submodule checkout.

- according to https://gitlab.com/gitlab-org/gitlab-runner/-/issues/3011#note_150604513 this might help

.gitlab-ci.yml

 variables:
-  GIT_SUBMODULE_STRATEGY: recursive
+  GIT_SUBMODULE_STRATEGY: none
 
 stages:
   - build
@@ -7,5 +7,8 @@ stages:
 test:
   image: openjdk:8
   stage: build
+  before_script:
+    - git submodule sync --recursive
+    - git submodule update --force --recursive
   script:
     - ./gradlew --no-daemon build