[3.12] gh-121735: Fix module-adjacent references in zip files (gh-123037)

[jaraco]

This PR is a selective backport of gh-123037, pulling only the fix and a one-off test to protect the behavior, but avoiding the test suite refactoring (which could not be backported as it also relies on other features only in Python 3.13).

• [3.12] Can't open orphan path on bare importlib.resources.files() under zipapp #121735: Fix module-adjacent references in zip files
• Backport the test capturing the behavior selectively.

[jaraco]

That's weird. The tests are failing in CI, but they're passing for me locally. I wonder why that is.

[jaraco]

That's weird. The tests are failing in CI, but they're passing for me locally. I wonder why that is.

The issue was twofold:

1. I failed to copy the whole fix, which requires changes to Lib/zipimport.py, which I'd missed because it was separated from the other crucial change by many changes to tests.
2. Because I was running the tests against a previous build, the zipimport hadn't been recompiled, so was still using a bootstrap zip importer with the needed changes.

Rebuilding cpython from scratch allowed the issue to replicate.