chore(deps): bump ajv and @microsoft/typespec-msgraph in /additions

Bumps [ajv](https://github.com/ajv-validator/ajv) to 8.20.0 and updates ancestor dependency [@microsoft/typespec-msgraph](https://github.com/microsoftgraph/typespec-msgraph). These dependencies need to be updated together.


Updates `ajv` from 8.17.1 to 8.20.0
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v8.17.1...v8.20.0)

Updates `@microsoft/typespec-msgraph` from 1.1.1 to 1.3.0
- [Commits](https://github.com/microsoftgraph/typespec-msgraph/commits)

---
updated-dependencies:
- dependency-name: ajv
  dependency-version: 8.20.0
  dependency-type: indirect
- dependency-name: "@microsoft/typespec-msgraph"
  dependency-version: 1.3.0
  dependency-type: direct:production
...

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Author: dependabot[bot]