Adds missing module_specs for usages of _LazyModule (#15230)

* Add missing __spec__ for transformers.models.auto

* Moves the __spec__-test to the UnitTest class

* Adds module_spec to all instances of _LazyModule

* Refactors an old test from pytest to unittest

templates/adding_a_new_model/cookiecutter-template-{{cookiecutter.modelname}}/__init__.py

@@ -210,4 +210,4 @@ if TYPE_CHECKING:
 else:
     import sys
 
-    sys.modules[__name__] = _LazyModule(__name__, globals()["__file__"], _import_structure)
+    sys.modules[__name__] = _LazyModule(__name__, globals()["__file__"], _import_structure, module_spec=__spec__)