Change Request: update ajv to 8.18.0

### ESLint version

10.0.0

### What problem do you want to solve?

ESLint currently uses version `6.12.4` of `ajv`. The authors of `ajv` have released version `8.18.0` to mitigate [CVE-2025-69873](https://nvd.nist.gov/vuln/detail/CVE-2025-69873).

I realise the [ESLint Security Policy](https://github.com/eslint/eslint/security/policy) mentions:
> there are no security concerns related to regular expression performance

So, there is no reason to hurry upgrading `ajv`, but in the long run I would still recommend upgrading `ajv` because:
1. the version used in ESLint was released 5+ years ago
2. ESLint is 2 major versions behind on `ajv`, which is no longer updated
3. even though a Regex DoS is very unlikely in the case of ESLint, ESLint is still reported to be vulnerable by tools used in enterprise organizations to scan dependencies

### What do you think is the correct solution?

Update `ajv` to `8.18.0` or higher.

### Participation

- [ ] I am willing to submit a pull request for this change.

### Additional comments

_No response_

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