[Backport release-23.11] quickgui: add quickemu to PATH

[github-actions]

Bot-based backport to release-23.11, triggered by a label in #268298.

• Before merging, ensure that this backport is acceptable for the release.
  • Even as a non-commiter, if you find that it is not acceptable, leave a comment.

[flexiondotorg]

I lead the upstream Quickemu project. I have tested these changes locally, and its an improvement to the user experience as Quickgui works as expected "out of the box" without additional knowledge of having to install quickemu.

Tested locally on NixOS 23.11.

[risicle]

CI failure for the cherry-pick reference

585cbc4 not found in any pickable branch

[flexiondotorg]

Given that this change has landed in unstable and 24.05 is imminent, I'll close this.