[Python][CI] Build failure with Cython 2

[pitrou]

Describe the bug, including details regarding any error messages, version, and platform.

These failures have appeared recently on the test-conda-python-3.10-cython2 Crossbow job:
https://github.com/ursacomputing/crossbow/actions/runs/10396692805/job/28791169422#step:7:3604

 Error compiling Cython file:
 ------------------------------------------------------------
 ...
 """

 cdef:
 c_string c_type_name = tobytes(type_name)
 c_string c_vendor_name = tobytes(vendor_name)
 shared_ptr[CDataType] c_type = make_shared[COpaqueType](
 ^
 ------------------------------------------------------------

 pyarrow/types.pxi:5331:63: Cannot assign type 'shared_ptr[COpaqueType]' to 'shared_ptr[CDataType]'

Component(s)

Continuous Integration, Python

[pitrou]

cc @lidavidm @jorisvandenbossche

[jorisvandenbossche]

FWIW, I think we should also consider simply raising the minimum cython version to something >= 3

[jorisvandenbossche]

Issue resolved by pull request 43765
#43765