Replace assertRaises with assertRaisesRegex in isbn_tests.py
assertRaises is not as good of a test as assertRaisesRegex.
The latter has an extra parameter to match the exception message,
allowing more precision when checking an error.
Change restored after revert in Ib41b30
Bug: T154281
Change-Id: Id67d5b76c0dc5a70289478d842cd3ebdc28b1b85