Pin Numpy < 2 in requirements

We have compiled extensions that are built against the Numpy C API.  The
Numpy transition guide for developers of downstream packages[^1]
encourages us to put in this pin until we have wheels built against the
newer version, which is not expected to be fully ABI compatible (but
extensions built against Numpy 2 _should_ work with older Numpys).

Note that this won't prevent package managers from resolving _older_
versions of Qiskit (which don't have the pin) along with Numpy 2, but
there's not a vast amount we can do about that now.

[^1]: numpy/numpy#24300

requirements.txt

@@ -1,5 +1,5 @@
 rustworkx>=0.13.0
-numpy>=1.17
+numpy>=1.17,<2
 ply>=3.10
 psutil>=5
 scipy>=1.5