tests: Pin numpy 2.4.0 for Python 3.14 CI tests

Add numpy==2.4.0 requirement for Python 3.14 (both default and
free-threaded builds). NumPy 2.4.0 is the first version to provide
official PyPI wheels for Python 3.14:

- numpy-2.4.0-cp314-cp314-manylinux_2_27_x86_64...whl (default)
- numpy-2.4.0-cp314-cp314t-manylinux_2_27_x86_64...whl (free-threaded)

Previously, CI was skipping all numpy-dependent tests for Python 3.14
because PIP_ONLY_BINARY was set and no wheels were available:

  SKIPPED [...] test_numpy_array.py:8: could not import 'numpy':
  No module named 'numpy'

With this change, the full numpy test suite will run on Python 3.14,
providing better test coverage for the newest Python version.

Note: Using exact pin (==2.4.0) rather than compatible release (~=2.4.0)
to ensure reproducible CI results with the first known-working version.

Author: rwgk

tests/requirements.txt

@@ -10,6 +10,7 @@ numpy~=1.22.2; platform_python_implementation=="CPython" and python_version=="3.
 numpy~=1.26.0; platform_python_implementation=="CPython" and python_version>="3.11" and python_version<"3.13" and platform_machine!="ARM64"
 numpy~=2.3.0; platform_python_implementation=="CPython" and python_version>="3.11" and platform_machine=="ARM64"
 numpy~=2.2.0; platform_python_implementation=="CPython" and python_version=="3.13" and platform_machine!="ARM64"
+numpy==2.4.0; platform_python_implementation=="CPython" and python_version>="3.14"
 pytest>=6
 pytest-timeout
 scipy~=1.5.4; platform_python_implementation=="CPython" and python_version<"3.10"