ci: add workflow_dispatch trigger to release drafter

[CaptainDriftwood]

Description

The Release Drafter workflow has failed with startup_failure on every run since it was added. Root cause: the repository's Actions policy only allowed GitHub-owned and Marketplace-verified actions, and release-drafter/release-drafter is neither, so GitHub refused to start the job:

The action release-drafter/release-drafter@b1476f6... is not allowed in CaptainDriftwood/python-icap because all actions must be from a repository owned by CaptainDriftwood, created by GitHub, or verified in the GitHub Marketplace.

That was fixed in repo settings (not code) by adding release-drafter/release-drafter@* to the allowed-actions patterns.

This PR adds a workflow_dispatch trigger so the drafter can be run manually — startup failures cannot be re-run, which made verifying the settings fix impossible without pushing a commit.

Type of Change

• CI

Testing

• This PR's pull_request event itself exercises the newly-allowlisted action

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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