fix(release): publish to PyPI by correcting semantic-release output name

[bartzbeielstein]

Problem

spotoptim's release.yml gates the Publish to PyPI step on
steps.release.outputs.new-release-published, but
cycjimmy/semantic-release-action@v4 exposes its outputs with underscores
(new_release_published). The hyphenated reference is always empty, so the step
has been silently skipped on every release — which is why the 0.11.x/0.12.x
series never reached PyPI (latest there is 0.10.3) even though the GitHub
Releases carried the built wheels.

Fix

Reference the correct new_release_published output. This fix: commit itself
cuts the next patch (0.12.4), and the corrected workflow will publish it to
PyPI — restoring PyPI as a resolvable source for downstreams that pin recent
spotoptim (e.g. spotforecast2 >= 0.12.3).

0.12.4 includes the steady-state inverse_transform fix already merged in
0.12.3 (#81), so a single PyPI publish unblocks parallel SpotOptim tuning
end-to-end.

Requires PyPI trusted-publishing (OIDC) to be configured for the spotoptim
project + this workflow (id-token: write is already set). If the publish
step fails on auth, the trusted publisher must be registered on PyPI.

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