pytest options moved into pyproject.toml (#18501)

Fixes this warning:

```
reading manifest template 'MANIFEST.in'
[…]
warning: no files found matching 'pytest.ini'
```

Author: mr-c

MANIFEST.in

@@ -42,7 +42,6 @@ graft test-data
 graft mypy/test
 include conftest.py
 include runtests.py
-include pytest.ini
 include tox.ini
 
 include LICENSE mypyc/README.md CHANGELOG.md