fix(release): compare normalized prerelease versions

[bokelley]

Summary

• compare the release manifest version after applying the same SemVer-to-PEP-440 normalization used by the release workflow
• keep stable-version comparisons unchanged

Root cause

Release Please stores 7.0.0-rc.1 in its manifest, while Python packaging correctly requires 7.0.0rc1 in pyproject.toml. The release configuration test compared these equivalent versions as raw strings, blocking the 7.0.0-rc.1 release PR.

Validation

• pytest tests/test_release_configuration.py tests/test_normalize_pyproject_prerelease.py: 6 passed
• Ruff and format checks passed
• full pre-commit suite passed

[aao-ipr-bot]

LGTM. Reuses the release workflow's own normalizer instead of re-encoding the SemVer→PEP-440 rule in the test — the assertion now checks the same transform that actually runs on the wire.

Things I checked

• Root cause is real. Release Please stores 7.0.0-rc.1 in .release-please-manifest.json; PEP 440 requires 7.0.0rc1 in pyproject.toml. The old raw-string compare blocked the RC release PR.
• The fix imports pep440_prerelease from scripts/normalize_pyproject_prerelease.py rather than duplicating the mapping — single source of truth with the code that normalizes pyproject.toml at release time.
• Stable-version path unchanged: pep440_prerelease returns input verbatim when _SEMVER_PRERELEASE_RE doesn't match, so 7.0.0 / 8.1.2 still compare as raw strings (normalize_pyproject_prerelease.py:27-34).
• Numbered prerelease maps correctly: 7.0.0-rc.1 → 7.0.0rc1, alpha/beta → a/b. Test-only diff, no source or public surface touched.
• Test-only change → skip-everything list, no experts.

Minor nits (non-blocking)

1. Numberless label passes through unnormalized. The regex requires -(alpha|beta|rc)\.(\d+), so a manifest value like 7.0.0-rc (no .N) returns unchanged — which is the current state of both files, so the assertion holds by identity rather than by normalization. Not this PR's job to fix, and release-please always emits the numbered form; worth a follow-up only if the manifest ever drifts to a bare label.

LGTM.