astral-sh/setup-uv no longer publishes floating major version tags

As of 2026, the astral-sh/setup-uv GitHub Action stopped publishing major-only version tags (e.g., @v8) for security reasons. Using @v8 will fail to resolve. This is a departure from the common GitHub Actions convention where actions provide floating major tags for automatic minor/patch updates.

Pin astral-sh/setup-uv to an exact version (e.g., @v8.0.0) instead of a major-only tag.