Update numpy requirement from <1.26,>=1.16.6 to >=1.16.6,<2.1 in /tests

Updates the requirements on [numpy](https://github.com/numpy/numpy) to permit the latest version.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/main/doc/RELEASE_WALKTHROUGH.rst)
- [Commits](numpy/numpy@v1.16.6...v2.0.0)

---
updated-dependencies:
- dependency-name: numpy
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

tests/constraints.txt

@@ -1,4 +1,4 @@
-numpy>=1.16.6,<1.26
+numpy>=1.16.6,<2.1
 attrs==23.1.0
 distro==1.8.0
 h5py>=3.1.0