Bump the build-npm group across 1 directory with 2 updates

Bumps the build-npm group with 2 updates in the /build/npm directory: [mocha](https://github.com/mochajs/mocha) and [sinon](https://github.com/sinonjs/sinon).


Updates `mocha` from 11.1.0 to 11.6.0
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/main/CHANGELOG.md)
- [Commits](mochajs/mocha@v11.1.0...v11.6.0)

Updates `sinon` from 20.0.0 to 21.0.0
- [Release notes](https://github.com/sinonjs/sinon/releases)
- [Changelog](https://github.com/sinonjs/sinon/blob/main/docs/changelog.md)
- [Commits](https://github.com/sinonjs/sinon/commits)

---
updated-dependencies:
- dependency-name: mocha
  dependency-version: 11.6.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: build-npm
- dependency-name: sinon
  dependency-version: 21.0.0
  dependency-type: direct:development
  update-type: version-update:semver-major
  dependency-group: build-npm
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]