Update providers.pyx

allow string imports outside of packages

Author: carloshorn

Diff for: src/dependency_injector/providers.pyx

@@ -5034,7 +5034,7 @@ def _resolve_calling_module():
 
 def _resolve_calling_package_name():
     module = _resolve_calling_module()
-    return module.__package__
+    return getattr(module, "__package__", None)
 
 
 cpdef _copy_parent(object from_, object to, dict memo):