[FEA]: Turn pytest warnings into errors

As suggested by @shwina here:

* https://github.com/NVIDIA/cccl/pull/3233#discussion_r1904059668

For easy future reference, this is the suggested pyproject.toml change:

* https://github.com/rapidsai/cudf/blob/955b1f4566abccf920a022dc78a1e654acf0de16/python/cudf/pyproject.toml#L97-L100

```
[tool.pytest.ini_options]
filterwarnings = [
"error",
"ignore:::.*xdist.*",
"ignore:::.*pytest.*",
]
```