Remove system-tests pin (#801)

Author: nccatoni

.github/workflows/system_tests.yml

@@ -28,13 +28,12 @@ jobs:
   system-tests:
     needs:
       - build
-    uses: DataDog/system-tests/.github/workflows/system-tests.yml@1e5d6b7096279ca43ce4826fda3cc805635b63c1
+    uses: DataDog/system-tests/.github/workflows/system-tests.yml@main
     permissions:
       contents: read
       id-token: write
     with:
       library: python_lambda
-      ref: 1e5d6b7096279ca43ce4826fda3cc805635b63c1
       binaries_artifact: binaries
       scenarios_groups: tracer_release
       skip_empty_scenarios: true