Bump cross-spawn, @yarnpkg/core and @yarnpkg/shell in /yarn2-plugins/…

…prune-dev-dependencies (#1356)

* Bump cross-spawn, @yarnpkg/core and @yarnpkg/shell

Bumps [cross-spawn](https://github.com/moxystudio/node-cross-spawn) to 7.0.6 and updates ancestor dependencies [cross-spawn](https://github.com/moxystudio/node-cross-spawn), [@yarnpkg/core](https://github.com/yarnpkg/berry/tree/HEAD/packages/yarnpkg-core) and [@yarnpkg/shell](https://github.com/yarnpkg/berry/tree/HEAD/packages/yarnpkg-shell). These dependencies need to be updated together.


Updates `cross-spawn` from 7.0.3 to 7.0.6
- [Changelog](https://github.com/moxystudio/node-cross-spawn/blob/master/CHANGELOG.md)
- [Commits](moxystudio/node-cross-spawn@v7.0.3...v7.0.6)

Updates `@yarnpkg/core` from 4.0.0-rc.26 to 4.1.6
- [Release notes](https://github.com/yarnpkg/berry/releases)
- [Changelog](https://github.com/yarnpkg/berry/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yarnpkg/berry/commits/@yarnpkg/core/4.1.6/packages/yarnpkg-core)

Updates `@yarnpkg/shell` from 4.0.0-rc.26 to 4.1.1
- [Release notes](https://github.com/yarnpkg/berry/releases)
- [Changelog](https://github.com/yarnpkg/berry/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yarnpkg/berry/commits/@yarnpkg/shell/4.1.1/packages/yarnpkg-shell)

---
updated-dependencies:
- dependency-name: cross-spawn
  dependency-type: indirect
- dependency-name: "@yarnpkg/core"
  dependency-type: direct:production
- dependency-name: "@yarnpkg/shell"
  dependency-type: indirect
...

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

* Update test spec

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Colin Casey <casey.colin@gmail.com>