ci: add --allow-same-version to pnpm version calls in release workflows (#1116)

## Summary

- Adds `--allow-same-version` flag to `pnpm version` calls in
`release.yaml` and `pre_release.yaml` workflows
- Prevents release failures when pnpm tries to set a version that is
already set (e.g. on re-runs or when the version hasn't changed)
- No functional change to the release process itself

## Testing

- Not run — CI-only change; correctness is verified by the release
workflows passing on next trigger