Switch system tests to a temp branch

Author: y9v

.github/workflows/system-tests.yml

@@ -24,9 +24,8 @@ on:
 env:
   REGISTRY: ghcr.io
   REPO: ghcr.io/datadog/dd-trace-rb
-  # Broken system-test: https://github.com/DataDog/system-tests/pull/3904
-  SYSTEM_TESTS_REF: 239c3eba6de0473817d3d88ebbc025c9d0c9574b
-  # SYSTEM_TESTS_REF: main # This must always be set to `main` on dd-trace-rb's master branch
+  # TODO: remove this change before merging to master
+  SYSTEM_TESTS_REF: enable-ip-blocking-for-ruby
 
 jobs:
   build-harness: