Bump @angular/core in /nifi-frontend/src/main/frontend

Bumps [@angular/core](https://github.com/angular/angular/tree/HEAD/packages/core) from 20.3.16 to 20.3.18.
- [Release notes](https://github.com/angular/angular/releases)
- [Changelog](https://github.com/angular/angular/blob/main/CHANGELOG.md)
- [Commits](https://github.com/angular/angular/commits/v20.3.18/packages/core)

---
updated-dependencies:
- dependency-name: "@angular/core"
  dependency-version: 20.3.18
  dependency-type: direct:production
...

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

Author: dependabot[bot]