gh-159044: Restore string conversion for HTTP tunnel headers

[SomSamantray]

HTTPSConnection.set_tunnel() regressed when it began calling .encode() directly on header names and values. Previously, formatting converted these values to strings, so values such as None and integers were accepted. Convert both names and values to strings before Latin-1 encoding, preserving that behavior and the existing CR/LF validation.

Fixes #159044

Tests

• ./python -m test test_httplib -m test_tunnel_headers_are_converted_to_strings — passed.
• ./python -m test test_httplib — passed (153 tests, 5 skipped).
• ./python Tools/patchcheck/patchcheck.py — passed.
• Full ./python -m test run: 449 test files passed, 96 skipped; failures were in test_os and test_pathlib mount/device assertions, test_socket VSOCK without a device, test_profiling (passed when rerun alone), and a shared-environment change reported by test_httpservers (passed alone).

AI tools assisted with investigation, implementation, and review. I reviewed the resulting changes.

• Issue: http.client.HTTPSConnection._tunnel raises AttributeError: 'NoneType' object has no attribute 'encode' when header value is None #159044

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #35071091 | 📁 Comparing 2311723 against main (c6c0608)

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2 files changed

± library/http.client.html
± whatsnew/changelog.html

[ZeroIntensity]

It is extremely rude to submit a PR after someone else has already done all the discussion, research, and asked to author the fix, especially if that someone is a first-time contributor. I'm closing this to give @bielpieroli a chance to work on a patch first.

[bielpieroli]

Thank you, @ZeroIntensity, I really appreciate it.

Sorry for the late reply. To be honest, when I woke up and saw a PR was already open I felt a bit discouraged, so I stayed away and only saw the notifications now.

I'll start working on the patch right now with my partner @LorenaMBorges :D