ci: fix scope prefix in beetmover apt task (#9905) (#9921)

Co-authored-by: Andrew Halberstadt <[email protected]>

taskcluster/config.yml

@@ -137,5 +137,10 @@ release-promotion:
         - toolchain
         - toolchain-openssl
 
+scriptworker:
+    scope-prefix: project:mozillavpn:releng
+
 shipit:
+    # TODO: Remove this when using mozilla-taskgraph 2.1 or higher. It'll use
+    # the 'scriptworker' config above then.
     scope-prefix: project:mozillavpn:releng:ship-it

taskcluster/mozillavpn_taskgraph/transforms/beetmover_apt.py

@@ -54,14 +54,13 @@ def beetmover_apt(config, tasks):
 
         if task["attributes"]["shipping-phase"] == "ship-client":
             bucket = "release"
-            project_name = "mozillavpn"
         else:
             bucket = "dep"
-            project_name = "mozillavpn:releng"
 
+        scope_prefix = config.graph_config["scriptworker"]["scope-prefix"]
         task["scopes"] = [
-            f"project:{project_name}:beetmover:apt-repo:{bucket}",
-            f"project:{project_name}:beetmover:action:import-from-gcs-to-artifact-registry"
+            f"{scope_prefix}:beetmover:apt-repo:{bucket}",
+            f"{scope_prefix}:beetmover:action:import-from-gcs-to-artifact-registry"
         ]
 
         task["label"] = f"beetmover-apt-{task['name']}"