GitLab

* Adding a valgrind build on debug Python 3.9
Co-authored-by: Boris Staletic <boris.staletic@gmail.com>

* Add Valgrind suppression files

- Introduce suppression file, populate it with a first suppression taken from CPython, and fix one leak in the tests
- Suppress leak in NumPy
- More clean tests!
- Tests with names a-e passing (except for test_buffer)
- Suppress multiprocessing errors
- Merge multiprocessing suppressions into other suppression files
- Numpy seems to be spelled with a big P
- Append single entry from valgrind-misc.supp to valgrind-python.supp, and make clear valgrind-python.supp is only CPython
Co-authored-by: Boris Staletic <boris.staletic@gmail.com>

* Enable test_virtual_functions with a workaround

* Add a memcheck cmake target

- Add a memcheck cmake target
- Reformat cmake
- Appease the formatting overlords - they are angry
- Format CMake valgrind target decently

* Update CI config to new action versions

* fix: separate memcheck from pytest

* ci: cleanup

* Merge Valgrind and other deadsnakes builds
Co-authored-by: Boris Staletic <boris.staletic@gmail.com>
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>

* Update pytest to 6.2.1 in tests/requirements.txt

* Pin pytest to last supported version for 3.5

* Suppress PytestUnraisableExceptionWarning and use sys.__unraisablehook__ instead of sys.unraisablehook

* Fix filterwarnings mark on old pytest and old Python versions

* Cleanup ignore_pytest_unraisable_warning decorator

Adds requirements file too.