ci(release): fix dry-run gate broken by github.event_name in reusable workflows

[d-laub]

Bug

The previous dry-run gate in release.yaml was:

```yaml

• name: Dry-run summary
  if: github.event_name == 'workflow_call' && inputs.dry_run == true
• name: Create GitHub release
  if: ${{ !(github.event_name == 'workflow_call' && inputs.dry_run == true) }}
  ```

In a reusable workflow invoked via workflow_call, github.event_name is the parent trigger (here, workflow_dispatch from release-pipeline.yaml), not workflow_call. So the condition was always false: Dry-run summary skipped, Create GitHub release ran.

The dry-run of run 26254656039 consequently created a real v0.25.0 tag and GH release with a placeholder body. The tag and release were manually cleaned up before this PR. PyPI publish, push-to-stable, and the bump commit were not affected — they correctly gate on inputs.dry_run directly.

Fix

Gate on inputs.dry_run directly. Also add dry_run to the workflow_dispatch input list so the standalone form supports dry-run too.

Test plan

• After merge, dispatch Release pipeline with increment=auto, dry_run=true and confirm release step shows Dry-run summary ✅ and Create GitHub release skipped.
• Confirm no v0.25.0 tag/release is created.