Bump ajv and @microsoft/api-extractor

Bumps [ajv](https://github.com/ajv-validator/ajv) to 8.18.0 and updates ancestor dependency [@microsoft/api-extractor](https://github.com/microsoft/rushstack/tree/HEAD/apps/api-extractor). These dependencies need to be updated together.


Updates `ajv` from 8.12.0 to 8.18.0
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v8.12.0...v8.18.0)

Updates `@microsoft/api-extractor` from 7.57.4 to 7.57.6
- [Changelog](https://github.com/microsoft/rushstack/blob/main/apps/api-extractor/CHANGELOG.md)
- [Commits](https://github.com/microsoft/rushstack/commits/@microsoft/api-extractor_v7.57.6/apps/api-extractor)

---
updated-dependencies:
- dependency-name: ajv
  dependency-version: 8.18.0
  dependency-type: direct:production
- dependency-name: "@microsoft/api-extractor"
  dependency-version: 7.57.6
  dependency-type: indirect
...

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Author: dependabot[bot]