Several tests failing on Guix

I'm working on packaging LibCST for Guix (https://guix.gnu.org), but several tests are failing (see full log at the bottom).

3 of them are failing with the same error message: `"No data_provider tests were created for test_type_availability! Please double check your data."`. Those are:
- libcst.metadata.tests.test_full_repo_manager
- libcst.metadata.tests.test_type_inference_provider
- libcst.tests.test_pyre_integration

The other is `libcst.codemod.tests.test_codemod_cli.TestCodemodCLI`, that fails because it cannot parse a piece of code.

Based on what I read in `tox.ini`, I run the tests using `python -m unittest`. I also had run `python3 -m libcst.codegen.generate visitors; python3 -m libcst.codegen.generate return_types` to fix 2 errors.

For the time being, I'll disable those tests, but any help in fixing those would be welcome!

```
======================================================================
ERROR: libcst.metadata.tests.test_full_repo_manager (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: libcst.metadata.tests.test_full_repo_manager
Traceback (most recent call last):
File "/gnu/store/q9rm8h9imazsq2c4qiv2yjpvlvliywqb-python-3.8.2/lib/python3.8/unittest/loader.py", line 436, in _find_test_path
module = self._get_module_from_name(name)
File "/gnu/store/q9rm8h9imazsq2c4qiv2yjpvlvliywqb-python-3.8.2/lib/python3.8/unittest/loader.py", line 377, in _get_module_from_name
__import__(name)
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/metadata/tests/test_full_repo_manager.py", line 11, in
from libcst.metadata.tests.test_type_inference_provider import _test_simple_class_helper
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/metadata/tests/test_type_inference_provider.py", line 14, in
from libcst.tests.test_pyre_integration import TEST_SUITE_PATH
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/tests/test_pyre_integration.py", line 95, in
class PyreIntegrationTest(UnitTest):
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/testing/utils.py", line 170, in __new__
populate_data_provider_tests(dct)
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/testing/utils.py", line 96, in populate_data_provider_tests
raise ValueError(
ValueError: No data_provider tests were created for test_type_availability! Please double check your data.

======================================================================
ERROR: libcst.metadata.tests.test_type_inference_provider (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: libcst.metadata.tests.test_type_inference_provider
Traceback (most recent call last):
File "/gnu/store/q9rm8h9imazsq2c4qiv2yjpvlvliywqb-python-3.8.2/lib/python3.8/unittest/loader.py", line 436, in _find_test_path
module = self._get_module_from_name(name)
File "/gnu/store/q9rm8h9imazsq2c4qiv2yjpvlvliywqb-python-3.8.2/lib/python3.8/unittest/loader.py", line 377, in _get_module_from_name
__import__(name)
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/metadata/tests/test_type_inference_provider.py", line 14, in
from libcst.tests.test_pyre_integration import TEST_SUITE_PATH
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/tests/test_pyre_integration.py", line 95, in
class PyreIntegrationTest(UnitTest):
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/testing/utils.py", line 170, in __new__
populate_data_provider_tests(dct)
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/testing/utils.py", line 96, in populate_data_provider_tests
raise ValueError(
ValueError: No data_provider tests were created for test_type_availability! Please double check your data.

======================================================================
ERROR: libcst.tests.test_pyre_integration (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: libcst.tests.test_pyre_integration
Traceback (most recent call last):
File "/gnu/store/q9rm8h9imazsq2c4qiv2yjpvlvliywqb-python-3.8.2/lib/python3.8/unittest/loader.py", line 436, in _find_test_path
module = self._get_module_from_name(name)
File "/gnu/store/q9rm8h9imazsq2c4qiv2yjpvlvliywqb-python-3.8.2/lib/python3.8/unittest/loader.py", line 377, in _get_module_from_name
__import__(name)
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/tests/test_pyre_integration.py", line 95, in
class PyreIntegrationTest(UnitTest):
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/testing/utils.py", line 170, in __new__
populate_data_provider_tests(dct)
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/testing/utils.py", line 96, in populate_data_provider_tests
raise ValueError(
ValueError: No data_provider tests were created for test_type_availability! Please double check your data.

======================================================================
FAIL: test_codemod_formatter_error_input (libcst.codemod.tests.test_codemod_cli.TestCodemodCLI)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/tmp/guix-build-python-libcst-0.3.7.drv-0/libcst-0.3.7/libcst/codemod/tests/test_codemod_cli.py", line 34, in test_codemod_formatter_error_input
self.assertIn(
AssertionError: 'error: cannot format -: Cannot parse: 13:10: async with AsyncExitStack() as stack:' not found in 'Finished codemodding 0 files!\n - Transformed 0 files successfully.\n - Skipped 0 files.\n - Failed to codemod 0 files.\n - 0 warnings were generated.\n'
```