GeezerVison

Summary

Treat a shebang line that cannot be decoded using zipapp.shebang_encoding as having no interpreter. Add a regression test for malformed shebang bytes and a Library NEWS entry.

Fixes #158546

Testing

• PYTHONPATH=Lib python3.15 -m unittest test.test_zipapp — 36 tests passed.
• Reproduced the reported UnicodeDecodeError against the unmodified source before the fix.
• git diff --check — passed.

The full CPython build/test matrix was not run; this change is limited to the pure-Python zipapp module and its tests.

AI assistance was used to inspect the issue and code, draft the focused change and test, and review the diff. I reproduced the original behavior and ran the tests listed above.

• Issue: zipapp.get_interpreter() raises UnicodeDecodeError on invalid shebang bytes #158546