Help test module should be in the Testing package

If you look at the info.yml file for a test module such as
drupal/core/modules/block/tests/modules_block_test
you will see that it has a line saying:

package: Testing

However, the help_test module in core/modules/help/test_modules/help_test is missing this line. There are tests that use this to detect "real" vs. "test" modules, so this line needs to be added to the help_test.info.yml file.