Bump @typespec/openapi from 1.2.1 to 1.3.0 in /additions (#866)

Bumps [@typespec/openapi](https://github.com/microsoft/typespec) from 1.2.1 to 1.3.0.
- [Release notes](https://github.com/microsoft/typespec/releases)
- [Commits](https://github.com/microsoft/typespec/commits/typespec-stable@1.3.0)

---
updated-dependencies:
- dependency-name: "@typespec/openapi"
  dependency-version: 1.3.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]