build(deps): bump ajv and @docusaurus/theme-mermaid

Bumps [ajv](https://github.com/ajv-validator/ajv) to 8.18.0 and updates ancestor dependency [@docusaurus/theme-mermaid](https://github.com/facebook/docusaurus/tree/HEAD/packages/docusaurus-theme-mermaid). These dependencies need to be updated together.


Updates `ajv` from 8.17.1 to 8.18.0
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v8.17.1...v8.18.0)

Updates `@docusaurus/theme-mermaid` from 3.8.1 to 3.9.2
- [Release notes](https://github.com/facebook/docusaurus/releases)
- [Changelog](https://github.com/facebook/docusaurus/blob/main/CHANGELOG.md)
- [Commits](https://github.com/facebook/docusaurus/commits/v3.9.2/packages/docusaurus-theme-mermaid)

---
updated-dependencies:
- dependency-name: ajv
  dependency-version: 8.18.0
  dependency-type: indirect
- dependency-name: "@docusaurus/theme-mermaid"
  dependency-version: 3.9.2
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]