test(conftest): make GPG-signing fixture work on Windows

[bearomorphism]

Description

Make the GPG-related bump tests work on Windows hosts where Gpg4win and Git for Windows ship separate gpg binaries with separate keyrings.

Currently, the tmp_commitizen_project_with_gpg fixture fails on a typical Windows developer machine for two reasons:

1. _get_gpg_keyid parses gpg --list-secret-keys output with a regex that only handles LF line endings. On Windows, gpg emits CRLF, so the regex never matches and the fixture asserts out at assert key_id.
2. Even when a fingerprint can be extracted, the test key is created by the gpg in PATH (Gpg4win, %APPDATA%\gnupg), but git commit -S invokes the gpg bundled with Git for Windows (~/.gnupg). That gpg can't find the secret key and signing fails with gpg: skipped "<fingerprint>": No secret key.

Changes

• Rewrite _get_gpg_keyid to parse the stable gpg --with-colons --list-secret-keys machine-readable format. Field 9 of the first fpr: line under a sec: block is the primary key fingerprint per the gpg DETAILS specification. This is line-ending agnostic.
• In tmp_commitizen_project_with_gpg, pin git config gpg.program to the absolute path of the gpg binary used to create the key (resolved via shutil.which("gpg")). This guarantees git uses the same gpg/keyring as the fixture on every platform.
• Add fpr to the codespell ignore list (pyproject.toml) so the gpg colon-output prefix used in the parser doesn't trip the spell check.

Behaviour on Linux / macOS is unchanged: shutil.which("gpg") returns the same gpg the subprocess call would have invoked anyway, and the --with-colons parser produces the same fingerprint as the previous regex.

Verification

Locally on Windows (Gpg4win 2.5.19 + Git for Windows 2.4.9):

• Before: test_bump_minor_increment_signed[*] and test_bump_minor_increment_signed_config_file[*] error out during fixture setup (4 errors).
• After: full suite passes — 1289 passed, 3 skipped, 2 xfailed.

Checklist

• uv run poe lint clean
• Existing test suite green locally on Windows

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.23%. Comparing base (4b93a50) to head (096da69).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1962   +/-   ##
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  Coverage   98.23%   98.23%           
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  Files          61       61           
  Lines        2779     2779           
=======================================
  Hits         2730     2730           
  Misses         49       49           

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