Fix resource sync orphan detection to exclude system user

This change resolves failing resource sync tests by ensuring the system user
is properly excluded from orphan detection during resource synchronization.

**Problem:**
Resource sync tests were failing because the system user (_system) was being
incorrectly identified as an "orphaned" resource and deleted during sync
operations. The issue was an inconsistency between:

1. The manifest endpoint (views.py) which already excluded system users
2. The orphan detection logic (sync.py) which did not exclude system users

This caused the system user to be absent from manifests but present in
orphan detection, leading to unintended deletion.

**Solution:**
- Added system user exclusion to get_orphan_resources() function
- Used get_system_user() utility for robust system user identification
- Filter by object_id rather than username for more reliable exclusion
- Maintains consistency with existing manifest endpoint behavior

**Impact:**
- Fixes 4 failing tests: test_resource_sync, test_delete_orphans,
  test_resource_sync_update_conflict, test_resource_sync_create_conflict
- Protects system user from being deleted during resource sync operations
- No impact on regular user resource synchronization behavior

Signed-off-by: Fabricio Aguiar <[email protected]>

rh-pre-commit.version: 2.3.2
rh-pre-commit.check-secrets: ENABLED

Author: fao89

ansible_base/resource_registry/tasks/sync.py

@@ -365,7 +365,7 @@ def get_orphan_resources(
     manifest_list: list[ManifestItem],
 ) -> QuerySet:
     """QuerySet with orphaned managed resources to be deleted."""
-    return (
+    queryset = (
         Resource.objects.filter(
             content_type__resource_type__name=resource_type_name,
         )
@@ -376,6 +376,16 @@ def get_orphan_resources(
         )
     )
 
+    # Exclude system user from deletion, consistent with manifest endpoint
+    if resource_type_name == "shared.user":
+        from ansible_base.lib.utils.models import get_system_user
+
+        system_user = get_system_user()
+        if system_user:
+            queryset = queryset.exclude(object_id=system_user.id)
+
+    return queryset
+
 
 def delete_resource(resource: Resource):
     """Wrapper to delete content_object and its related Resource.