Use numpy 1.26b for cp312

like scipy

pyproject.toml

@@ -1,9 +1,17 @@
 [build-system]
-requires = ["setuptools",
-            "setuptools_scm>=6.2",
-            "cython==0.29.34",
-            "numpy>=1.25,<2",
-            "extension-helpers"]
+requires = [
+    "setuptools",
+    "setuptools_scm>=6.2",
+    "cython==0.29.34",
+    "numpy>=1.25,<2",
+
+    # For Python versions which aren't yet officially supported, we specify an
+    # unpinned NumPy which allows source distributions to be used and allows
+    # wheels to be used as soon as they become available.
+    "numpy>=1.26.0b1; python_version>='3.12'",
+
+    "extension-helpers"
+]
 build-backend = 'setuptools.build_meta'
 
 [tool.setuptools_scm]