GH-39537: [Packaging][Python] Add a numpy<2 pin to the install requir…

…ements for the 15.x release branch (#39538)

### Rationale for this change

PyArrow wheels for the 15.0.0 release will not be compatible with future numpy 2.0 packages, therefore it is recommended to add this upper pin now for _releases_. We will keep the more flexible pin on the development branch (by reverting this commit on main, but so it can be cherry-picked in the release branch)

* Closes: #39537

Authored-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Signed-off-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>

python/setup.py

@@ -449,7 +449,7 @@ def has_ext_modules(foo):
 
 
 install_requires = (
-    'numpy >= 1.16.6',
+    'numpy >= 1.16.6, <2',
 )