feat: Also pass TERMINFO when in an interactive shell

[edgarrmondragon]

Ghostty uses TERMINFO, instead of installing into the terminfo database, to advertise terminal capabilities. The Ghostty docs instructs users to configure tools (e.g. ssh) which sanitize their environment variables to preserve this variable.

Without this change, I'm seeing

$ tox -e 3.14
3.14: uv-sync> /Users/work/.local/share/uv/tools/tox/bin/uv sync --locked --python-preference system --no-default-groups --group tests -p cpython3.14
3.14: commands[0]> coverage run -m pytest tests
No entry for terminal type "xterm-ghostty";
using dumb terminal settings.
================ test session starts ================
platform darwin -- Python 3.14.5, pytest-9.0.3, pluggy-1.6.0

Ghostty docs: https://ghostty.org/docs/help/terminfo

• ran the linter to address style issues (tox -e fix)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added news fragment in docs/changelog folder
• updated/extended the documentation