chore: pin third-party GitHub Actions to commit SHAs (#59)

## Summary

Pin all third-party GitHub Actions to full-length commit SHAs to prevent
supply chain attacks.

Addresses findings from the
[`third-party-action-not-pinned-to-commit-sha`](https://github.com/launchdarkly/semgrep-rules/blob/main/github-actions/third-party-action-not-pinned-to-commit-sha.yml)
Semgrep rule.

## Test plan

- [ ] Verify CI passes with pinned action SHAs

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: workflow-only changes that pin action references; main risk
is CI/release breakage if a pinned SHA is incorrect or later removed
upstream.
> 
> **Overview**
> Pins previously tag-based third-party GitHub Actions in
`manual-publish.yml` and `release-please.yml` to specific commit SHAs
(notably `release-please-action` and `gh-action-pypi-publish`) to reduce
GitHub Actions supply-chain risk.
> 
> Adds inline version comments for the pinned actions; no functional
build/release logic changes beyond the pinned references.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
e4ae025. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: pkaeding

.github/workflows/manual-publish.yml

@@ -22,7 +22,7 @@ jobs:
           python-version: 3.9
 
       - name: Install poetry
-        uses: abatilo/actions-poetry@7b6d33e44b4f08d7021a1dee3c044e9c253d6439
+        uses: abatilo/actions-poetry@7b6d33e44b4f08d7021a1dee3c044e9c253d6439 # v3.0.0
 
       - uses: launchdarkly/gh-actions/actions/release-secrets@release-secrets-v1.2.0
         name: "Get PyPI token"
@@ -34,6 +34,6 @@ jobs:
 
       - name: Publish package distributions to PyPI
         if: ${{ inputs.dry_run == false }}
-        uses: pypa/gh-action-pypi-publish@release/v1
+        uses: pypa/gh-action-pypi-publish@ed0c53931b1dc9bd32cbe73a98c7f6766f8a527e # release/v1
         with:
           password: ${{env.PYPI_AUTH_TOKEN}}

.github/workflows/release-please.yml

@@ -13,7 +13,7 @@ jobs:
       contents: write # Contents and pull-requests are for release-please to make releases.
       pull-requests: write
     steps:
-      - uses: googleapis/release-please-action@v4
+      - uses: googleapis/release-please-action@16a9c90856f42705d54a6fda1823352bdc62cf38 # v4
         id: release
 
       - uses: actions/checkout@v4
@@ -28,7 +28,7 @@ jobs:
 
       - name: Install poetry
         if: ${{ steps.release.outputs.releases_created == 'true' }}
-        uses: abatilo/actions-poetry@7b6d33e44b4f08d7021a1dee3c044e9c253d6439
+        uses: abatilo/actions-poetry@7b6d33e44b4f08d7021a1dee3c044e9c253d6439 # v3.0.0
 
       - uses: launchdarkly/gh-actions/actions/release-secrets@release-secrets-v1.2.0
         name: "Get PyPI token"
@@ -45,6 +45,6 @@ jobs:
 
       - name: Publish package distributions to PyPI
         if: ${{ steps.release.outputs.releases_created == 'true' }}
-        uses: pypa/gh-action-pypi-publish@release/v1
+        uses: pypa/gh-action-pypi-publish@ed0c53931b1dc9bd32cbe73a98c7f6766f8a527e # release/v1
         with:
           password: ${{env.PYPI_AUTH_TOKEN}}