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

Author: nccatoni

.github/workflows/run-system-tests.yaml

@@ -62,7 +62,7 @@ jobs:
     needs:
     - build
     # If you change the following comment, update the pattern in the update_system_test_reference.sh script to match.
-    uses: DataDog/system-tests/.github/workflows/system-tests.yml@main # system tests are pinned on release branches only
+    uses: DataDog/system-tests/.github/workflows/system-tests.yml@1e5d6b7096279ca43ce4826fda3cc805635b63c1 # system tests are pinned on release branches only
     permissions:
       id-token: write
     with: