Switch system-tests to branch with tests enabled

Author: Strech

.github/workflows/system-tests.yml

@@ -22,7 +22,7 @@ permissions: {}
 env:
   REGISTRY: ghcr.io
   REPO: ghcr.io/datadog/dd-trace-rb
-  SYSTEM_TESTS_REF: main # This must always be set to `main` on dd-trace-rb's master branch
+  SYSTEM_TESTS_REF: appsec-57504-enable-session-tracking-and-fingerprinting # This must always be set to `main` on dd-trace-rb's master branch
 
 jobs:
   changes: