gh-154892: Fix PyLong_AsLong() error checks in _zoneinfo

[BHUVANSH855]

Summary

Fix Modules/_zoneinfo.c:get_local_timestamp() to correctly distinguish a legitimate -1 result from PyLong_AsLong() from an actual conversion error by checking PyErr_Occurred(), matching the documented C API behavior and the pure-Python implementation.

The previous implementation treated any -1 return value from PyLong_AsLong() as an error, even when no exception was set. This caused datetime subclasses overriding hour, minute, or second to return -1 to incorrectly raise an exception in the C accelerator.

This PR also adds a regression test covering datetime subclasses whose hour, minute, and second properties return -1.

Issue

Closes issue gh-154892

[johnslavik]

I'll change "Closes: gh-154892" in your PR description to "Closes issue gh-154892", because the use of "closes" keyword would close the issue immediately after this PR is merged and before 3 other backport PRs of your change to our maintenance branches are merged. We want to close the issue after the backport PRs are merged.