Fix the test command didn't discover PEPManagementCommandTests

[mozillazg]

Before:

$ ./manage.py test peps/tests -v2
Creating test database for alias 'default' ('test_pythondotorg')...
....
System check identified no issues (0 silenced).
test_add_image_not_found (peps.tests.test_converters.PEPConverterTests) ... ok
test_html_do_not_prettify (peps.tests.test_converters.PEPConverterTests) ... ok
test_invalid_pep_number (peps.tests.test_converters.PEPConverterTests) ... ok
test_source_link (peps.tests.test_converters.PEPConverterTests) ... ok
test_source_link_rst (peps.tests.test_converters.PEPConverterTests) ... ok
test_strip_html_and_body_tags (peps.tests.test_converters.PEPConverterTests) ... ok

----------------------------------------------------------------------
Ran 6 tests in 0.203s

OK
Destroying test database for alias 'default' ('test_pythondotorg')...

After:

$ ./manage.py test peps/tests -v2
Creating test database for alias 'default' ('test_pythondotorg')...
...
System check identified no issues (0 silenced).
test_dump_pep_pages (peps.tests.test_commands.PEPManagementCommandTests) ... ok
test_generate_pep_pages_real (peps.tests.test_commands.PEPManagementCommandTests) ... ok
test_image_generated (peps.tests.test_commands.PEPManagementCommandTests) ... ok
test_add_image_not_found (peps.tests.test_converters.PEPConverterTests) ... ok
test_html_do_not_prettify (peps.tests.test_converters.PEPConverterTests) ... ok
test_invalid_pep_number (peps.tests.test_converters.PEPConverterTests) ... ok
test_source_link (peps.tests.test_converters.PEPConverterTests) ... ok
test_source_link_rst (peps.tests.test_converters.PEPConverterTests) ... ok
test_strip_html_and_body_tags (peps.tests.test_converters.PEPConverterTests) ... ok

----------------------------------------------------------------------
Ran 9 tests in 1.194s

OK
Destroying test database for alias 'default' ('test_pythondotorg')...

Ref #1389

[berkerpeksag]

LGTM, thanks! Please leave a comment after you've addressed review comments. GitHub doesn't send any notifications when you force-pushed to a branch.