ci: build releases on Python 3.13 so poetry installs

[devin-ai-integration]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

• Failed 1.2.1 release run: https://github.com/launchdarkly/python-server-sdk-otel/actions/runs/34408713290/attempts/1
• Failed manual publish after pinning poetry to 1.8.5 (ci: Pin poetry to 1.8.5 in the release workflows #56): https://github.com/launchdarkly/python-server-sdk-otel/actions/runs/34501023236/job/102951560951

Describe the solution you've provided

Both release workflows ran actions/setup-python with python-version: 3.9 and then installed poetry into that interpreter, so the Install poetry step now fails with:

Fatal error from pip prevented installation.
    TypeError: dataclass() got an unexpected keyword argument 'slots'

setup-python upgrades pip in the selected interpreter (log shows Successfully installed pip-26.0.1), and pip 26 requires Python >= 3.10 — dataclass(slots=...) is 3.10+ — so pipx can no longer install poetry under 3.9 at any poetry version. This is why pinning poetry-version: 1.8.5 in #56 did not help.

This bumps the release/publish interpreter to 3.13. Release builds only run poetry build and make docs, neither of which needs the oldest supported interpreter, and the produced wheel/sdist keep python = ">=3.9" from pyproject.toml. ci.yml still tests 3.9–3.13 and is unaffected (it installs poetry before setup-python, using the runner's default interpreter, which is why CI stayed green).

Note: 1.2.1 was never published — PyPI is still at 1.2.0 — so after this merges the Publish Package workflow needs to be re-run for 1.2.1.

Describe alternatives you've considered

• Move Install poetry before setup-python, as ci.yml does, so poetry installs into the runner's default interpreter. Works, but leaves the release step implicitly dependent on step ordering.
• Pin poetry (already done in ci: Pin poetry to 1.8.5 in the release workflows #56) — insufficient, since the failure comes from pip on 3.9, not the poetry version.

Additional context

Same 3.9 setup existed in release-please.yml and manual-publish.yml; both are updated.

Link to Devin session: https://app.devin.ai/sessions/27c11423375c4470807e81afc8567bb1
Open in Devin Desktop: https://app.devin.ai/desktop/session/27c11423375c4470807e81afc8567bb1?variant=devin

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Note

Overview
Fixes broken release and manual publish jobs by running actions/setup-python with Python 3.13 instead of 3.9 in manual-publish.yml and release-please.yml.

setup-python pulls in pip 26, which needs Python ≥ 3.10, so installing Poetry under 3.9 fails (dataclass(slots=...)). Release steps only use Poetry to build and publish; wheel/sdist metadata still targets python >= 3.9 from pyproject.toml, and ci.yml matrix testing is unchanged.

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[devin-ai-integration]

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