ci: test against numpy v2 (#695)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Chores**
- Streamlined the optional dependencies section by removing extraneous
comments in the configuration file.
- The `test` dependency now clearly specifies `"numpy<2"` without
additional notes.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

pyproject.toml

@@ -42,9 +42,6 @@ dpdata = "dpdata.cli:dpdata_cli"
 
 [project.optional-dependencies]
 test = [
-    # https://github.com/materialsproject/pymatgen/issues/3882
-    # https://github.com/kuelumbus/rdkit-pypi/issues/102
-    "numpy<2",
 ]
 ase = ['ase']
 amber = [