fix: upgrade 'testing-preview' VM

With 2x RAM available: from 'e2-standard-8' to 'e2-highmem-8'.

Author: jpraynaud

.github/workflows/ci.yml

@@ -584,7 +584,7 @@ jobs:
             terraform_backend_bucket: hydra-terraform-admin
             google_region: europe-west1
             google_zone: europe-west1-b
-            google_machine_type: e2-standard-8
+            google_machine_type: e2-highmem-8
             google_compute_instance_boot_disk_size: 200
             google_compute_instance_data_disk_size: 250
           - environment: testing-sanchonet