[CI][Packaging][Python] Python 3.15.0.rc*: add testing against Pandas nightly builds

[paultiq]

Describe the enhancement requested

This issue is to add Pandas to the 3.15.0 nightly builds:

Background

#48191 added builds for 3.15.0.rc1, but disabled Pandas which was not yet available.

Pandas nightly builds now include 3.15.0: Pandas: TRACKER: support for Python 3.15

Changes Required

See comment #48191 (comment) for required changes.

Component(s)

Continuous Integration, Python

[EwoutH]

Wheels on PyPI would also be great, so that downstream dependencies can start testing their own packages.

[paultiq]

This issue is just about adding the Pandas nightly index, to improve test coverage.

PyArrow nightly builds are here, including 3.15 support: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pyarrow/