Custom mix task to retry failed tests once in CI pipeline

This will be temporary* as we hunt down the cause of the random test failures

* gonna regret this

.gitlab-ci.yml

@@ -135,7 +135,7 @@ unit-testing-1.13.4-otp-25:
   script: &testing_script
     - mix ecto.create
     - mix ecto.migrate
-    - mix test --cover --preload-modules
+    - mix pleroma.test_runner --cover --preload-modules
   coverage: '/^Line total: ([^ ]*%)$/'
   artifacts:
     reports:
@@ -165,7 +165,7 @@ unit-testing-1.13.4-otp-25-erratic:
   script:
     - mix ecto.create
     - mix ecto.migrate
-    - mix test --only=erratic
+    - mix pleroma.test_runner --only=erratic
 
 formatting-1.15:
   extends: .build_changes_policy