Bump drf-yasg from 1.20.0 to 1.21.3 in /api

Bumps [drf-yasg](https://github.com/axnsan12/drf-yasg) from 1.20.0 to 1.21.3.
- [Release notes](https://github.com/axnsan12/drf-yasg/releases)
- [Changelog](https://github.com/axnsan12/drf-yasg/blob/1.21.3/docs/changelog.rst)
- [Commits](axnsan12/drf-yasg@1.20.0...1.21.3)

---
updated-dependencies:
- dependency-name: drf-yasg
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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