Bump grunt from 1.3.0 to 1.5.2 in /tests/dummy

Bumps [grunt](https://github.com/gruntjs/grunt) from 1.3.0 to 1.5.2.
- [Release notes](https://github.com/gruntjs/grunt/releases)
- [Changelog](https://github.com/gruntjs/grunt/blob/main/CHANGELOG)
- [Commits](gruntjs/grunt@v1.3.0...v1.5.2)

---
updated-dependencies:
- dependency-name: grunt
  dependency-type: direct:production
...

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Author: dependabot[bot]