[sparsity] Fix for the failing pruner test (#68794)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68794
The pruner `test_constructor` fails because of a typo in the regular expression matching for the error that the pruner throws.
This fixes it.
Test Plan:
Separate test is not needed -- single letter change.
Previous test: `python test/test_ao_sparsity.py -- TestBasePruner
Reviewed By: ngimel
Differential Revision: D32609589
Pulled By: z-a-f
fbshipit-source-id: 800ef50c8cdbf206087bc6f945d1830e4af83c03
