It is possible to set up a semi-automated test. Since Colab requires a Google account and authorization to run, I don't know whether a GitHub YAML bot could use it. However, you could automate most of the workflow and manually trigger the test on a personal Colab notebook, much like you manually trigger a @swift-ci workflow.
Modify my build script to pull from the nightly build, and add some Swift scripts that you can download into a Colab notebook. You need to be cautious about build times, as you will be kicked off of Colab if one task takes too long. However, what you are thinking of is entirely doable.
Once I have Colab fully functional again (or the best it can possibly get), I'm going to switch to MetalXLA and be fully occupied with finishing it before PyTorch releases their Metal backend. When that happens, you could work on some testing scripts and try them out in Colab.