Bump OpenTimelineIO from 4440afa to 21bd2c9

Bumps [OpenTimelineIO](https://github.com/PixarAnimationStudios/OpenTimelineIO) from `4440afa` to `21bd2c9`.
- [Release notes](https://github.com/PixarAnimationStudios/OpenTimelineIO/releases)
- [Commits](AcademySoftwareFoundation/OpenTimelineIO@4440afa...21bd2c9)

---
updated-dependencies:
- dependency-name: OpenTimelineIO
  dependency-version: 21bd2c9dbbcdb4347bbe259104492978b0d8a77b
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]