test(.github/workflows): pin system-tests for making sure we pass them

Author: darccio

.github/workflows/system-tests.yml

@@ -127,7 +127,7 @@ jobs:
         uses: actions/checkout@v3
         with:
           repository: 'DataDog/system-tests'
-          ref: ${{ inputs.ref }}
+          ref: dario.castane/langplat-286/origin-detection
 
       - name: Checkout dd-trace-go
         uses: actions/checkout@v3