Lazy import triggers C assert if reading `spec._initializing` raises

[encukou]

Bug report

Bug description:

This has been crashing in debug mode since the initial lazy import implementation:

import sys
import types

class Spec:
    @property
    def _initializing(self):
        raise RuntimeError("boom")

module = types.ModuleType("cached_spec")
module.__spec__ = Spec()
module.attr = 1
sys.modules["cached_spec"] = module

# This line fails, but cannot be in a try block:
lazy from cached_spec import attr

python3.15d: /builddir/build/BUILD/python3.15-3.15.0_rc2-build/Python-3.15.0rc2/Python/generated_cases.c.h:7979: _PyEval_EvalFrameDefault: Assertion `!_PyErr_Occurred(tstate)' failed.
Aborted                    (core dumped) python3.15d /tmp/repro.py

CPython versions tested on:

3.15, CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-158402: Clear error if PyImport_GetModule raises in lazy import #158403