chore(ci): pin system-tests workflow to 1e5d6b709

Author: nccatoni

.github/workflows/system_tests.yml

@@ -28,7 +28,7 @@ jobs:
   system-tests:
     needs:
       - build
-    uses: DataDog/system-tests/.github/workflows/system-tests.yml@main
+    uses: DataDog/system-tests/.github/workflows/system-tests.yml@1e5d6b7096279ca43ce4826fda3cc805635b63c1
     secrets:
       DD_API_KEY: ${{ secrets.DD_API_KEY }}
       TEST_OPTIMIZATION_API_KEY: ${{ secrets.TEST_OPTIMIZATION_API_KEY }}