chore(ci): use dd-sts for system-tests test optimization (#306)

* chore(ci): use dd-sts for system-tests test optimization

* chore(ci): remove dd_sts_policy from system-tests subworkflow

* chore(ci): remove unneeded permissions from system-tests subworkflow

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

* fix: add contents:read permission to system-tests workflow call

* chore(ci): pass ref to system-tests reusable workflow

Author: nccatoni

.github/workflows/dev.yml

@@ -197,14 +197,15 @@ jobs:
 
   system-tests:
     needs: build-system-tests-artifact
-    uses: DataDog/system-tests/.github/workflows/system-tests.yml@main
+    uses: DataDog/system-tests/.github/workflows/system-tests.yml@1e5d6b7096279ca43ce4826fda3cc805635b63c1
     secrets:
       TEST_OPTIMIZATION_API_KEY: ${{ secrets.DD_CI_VIS_API_KEY }}
     permissions:
       contents: read
-      packages: write
+      id-token: write
     with:
       library: cpp
+      ref: 1e5d6b7096279ca43ce4826fda3cc805635b63c1
       binaries_artifact: system_tests_binaries
       parametric_job_count: 8  # dedicated parameter to speed up parametric job
       scenarios: PARAMETRIC