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

Author: nccatoni

.github/workflows/system_tests.yml

@@ -30,6 +30,7 @@ jobs:
       - build
     uses: DataDog/system-tests/.github/workflows/system-tests.yml@1e5d6b7096279ca43ce4826fda3cc805635b63c1
     permissions:
+      contents: read
       id-token: write
     with:
       library: python_lambda