Normalize TLS server hostnames

[bubaizhanshen]

Summary

Fixes #1063.

Hostnames may include a trailing dot to mark a fully qualified domain name. Passing that dotted hostname to TLS verification can cause a certificate hostname mismatch even when the certificate is valid for the same hostname without the final dot.

This strips trailing dots from server_hostname in the sync, anyio, and trio TLS backends before passing the name to the TLS layer.

Tests:

• pytest tests/test_ssl.py
• pytest tests/_sync/test_connection.py tests/_async/test_connection.py
• ruff check httpcore/_ssl.py httpcore/_backends/sync.py httpcore/_backends/anyio.py httpcore/_backends/trio.py tests/test_ssl.py
• ruff format --check httpcore/_ssl.py httpcore/_backends/sync.py httpcore/_backends/anyio.py httpcore/_backends/trio.py tests/test_ssl.py
• python -m py_compile httpcore/_ssl.py httpcore/_backends/sync.py httpcore/_backends/anyio.py httpcore/_backends/trio.py tests/test_ssl.py
• git diff --check

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• Documentation does not need an update for this change.