MAINT: Remove legacy hook marks

[mtsokol]

Hi!
When running the test suite I get an error when collecting tests:

pytest.PytestDeprecationWarning: The hookimpl pytest_json_modifyreport uses old-style configuration options (marks or attributes).
Please use the pytest.hookimpl(optionalhook=True) decorator instead
 to configure the hooks.
 See https://docs.pytest.org/en/latest/deprecations.html#configuring-hook-specs-impls-using-markers
 at /home/runner/work/numpy/numpy/array-api-tests/reporting.py:94
Error: Process completed with exit code 1.

The first CI run in my fork: https://github.com/mtsokol/numpy/actions/runs/6894487016/job/18756394760

Here's a small patch that updates decorators.

[asmeurer]

Should verify this manually. I don't think we generate JSON on CI.

[honno]

Thanks for the PR!! Closing this though as its resolved by #218 now.