I've been using act[1] as a tool to develop/test actions locally, which has helped a lot for creating new actions and debugging existing ones without incurring additional build costs.
There does appear to be some solutions on the marketplace that will allow you to ssh into a runner, but I haven't had a need for them as of yet.
If folks do need to SSH into a runner to get over some humps, come and talk to me. No point in waiting to get to that 5 or 25 minute mark in a job just to change one line and have to wait again.
If folks need to SSH into a runner to debug stuff, don't talk to me nor anyone else, just chose a CI that allow you to do that without any extras nor 3rd party stuff :) CircleCI is great for that, but also Woodpecker CI ships a "run locally" command with their CLI as well, and as a huge plus, Woodpecker is 100% open source, compared to most other stuff.
There does appear to be some solutions on the marketplace that will allow you to ssh into a runner, but I haven't had a need for them as of yet.
[1] https://github.com/nektos/act