ci: fix release drafter race condition

[aaronsteers]

Summary

Fixes a race condition in the release-drafter workflow where merged PRs sometimes don't appear in the draft release notes when multiple PRs merge in quick succession.

Changes:

1. Add concurrency group with cancel-in-progress: false to queue (not cancel) overlapping runs
2. Pin to @v6.0.0 to avoid v6.1.0 bug where the action fails to find existing draft releases and creates duplicates

Review & Testing Checklist for Human

• Verify release-drafter#1425 is still open before merging
• After merging, test by merging 2-3 PRs in quick succession and verify all appear in the draft release

Notes

• Same fix already applied to airbyte-ops-mcp and awesome-python-template repos
• Requested by: AJ Steers (@aaronsteers)
• Link to Devin run: https://app.devin.ai/sessions/0dafc41101d144fe975937184b356eb3

[devin-ai-integration]

Original prompt from AJ Steers

Received message in Slack channel #ask-devin-ai:

@Devin - checks to see if any of them need this fix: <https://github.com/airbytehq/airbyte-ops-mcp/pull/183|https://github.com/airbytehq/airbyte-ops-mcp/pull/183>
Thread URL: https://airbytehq-team.slack.com/archives/C08BHPUMEPJ/p1767303466854019

[devin-ai-integration]

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