BLD: Use numpy2.0.0rc1 to build the package

This will still work with older numpy versions when running
Cartopy built from a wheel with this build requirement.

pyproject.toml

@@ -3,7 +3,13 @@ requires = [
     "wheel",
     "setuptools >= 40.6.0",
     "Cython >= 0.29.24",
-    "oldest-supported-numpy",
+    # numpy requirement for wheel builds for distribution on PyPI - building
+    # against 2.x yields wheels that are also compatible with numpy 1.x at
+    # runtime.
+    # Note that building against numpy 1.x works fine too - users and
+    # redistributors can do this by installing the numpy version they like and
+    # disabling build isolation.
+    "numpy>=2.0.0rc1",
     "setuptools_scm >= 7.0.0",
 ]
 build-backend = "setuptools.build_meta"