Fix failing E2E tests for folders (#1884)

* Run tests requiring uniqueness on org level serially (organization tags, firewall policies)
* make gcs bucket name globally unique

---------

Co-authored-by: Ludovico Magnocavallo <ludomagno@google.com>

modules/folder/README.md

@@ -196,7 +196,7 @@ module "folder" {
     policy = module.firewall-policy.id
   }
 }
-# tftest modules=2 resources=3 e2e
+# tftest modules=2 resources=3 e2e serial
 ```
 ## Log Sinks
 
@@ -204,6 +204,7 @@ module "folder" {
 module "gcs" {
   source        = "./fabric/modules/gcs"
   project_id    = var.project_id
+  prefix        = var.prefix
   name          = "gcs_sink"
   force_destroy = true
 }
@@ -316,7 +317,7 @@ module "folder" {
     env-prod = module.org.tag_values["environment/prod"].id
   }
 }
-# tftest modules=2 resources=5 inventory=tags.yaml e2e
+# tftest modules=2 resources=5 inventory=tags.yaml e2e serial
 ```
 
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