Bump ajv in /react-frontend (#270)

Bumps  and [ajv](https://github.com/ajv-validator/ajv). These dependencies needed to be updated together.

Updates `ajv` from 6.12.6 to 6.15.0
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v6.12.6...v6.15.0)

Updates `ajv` from 8.16.0 to 8.18.0
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v6.12.6...v6.15.0)

---
updated-dependencies:
- dependency-name: ajv
  dependency-version: 6.15.0
  dependency-type: indirect
- dependency-name: ajv
  dependency-version: 8.18.0
  dependency-type: indirect
...

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Author: dependabot[bot]