ci: install poetry before setup-python in release workflows

[devin-ai-integration]

Installs poetry before actions/setup-python in both release workflows, matching ci.yml, so the release build keeps Python 3.9.

• Fixes the Install poetry failure in release-please.yml and manual-publish.yml (latest occurrence: https://github.com/launchdarkly/python-server-sdk-otel/actions/runs/34501023236/job/102951560951)
• No version changes: poetry-version: "1.8.5" and python-version: 3.9 stay as they are
• 1.2.1 was never published (PyPI is still at 1.2.0), so Publish Package needs a re-run once this merges

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

Implementation details

Root cause: with setup-python first, the poetry action's pipx install runs under the 3.9 interpreter that setup-python just provisioned — and setup-python upgrades pip in that interpreter (Successfully installed pip-26.0.1 in the job log). pip 26 no longer supports 3.9, so pipx fails with TypeError: dataclass() got an unexpected keyword argument 'slots' (that kwarg is 3.10+). This is version-independent for poetry, which is why pinning poetry-version: "1.8.5" in #56 did not fix it.

Why ci.yml stayed green: it installs poetry first, so pipx uses the runner image's interpreter — the 3.9 matrix job logs installed package poetry 1.8.5, installed using Python 3.12.3 — and setup-python then provisions 3.9 for the steps that follow. This PR gives the release workflows the same ordering, so poetry itself runs on the image python while poetry build / make docs still execute against 3.9.

Alternative rejected: bumping the release interpreter to 3.13 (#57, closed) — it works, but drops 3.9 from the release path unnecessarily.

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
Reorders steps in manual-publish.yml and release-please.yml so Install poetry runs before actions/setup-python, matching ci.yml.

This fixes release jobs that failed when poetry was installed via pipx after setup-python had upgraded pip on Python 3.9 (pip 26 + 3.9 incompatibility). Poetry now installs using the runner’s default interpreter; Python 3.9 and poetry 1.8.5 are unchanged for build/publish steps.

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