I contribute to various OSS (and private) projects all time just by using the GitHub code editor and catching errors or regressions if any in the CI. Having a fully fledged dev environment is even better.
Basically it's just the same as whipping out a simple text editor in hurry; if I need to modify multiple files, I just do multiple commits (do a change -> commit -> jump to my branch/fork -> do the rest of the changes one by one) as GitHub doesn't support editing multiple files for a single commit and then I wait for the CI results. If something goes awry I'll probably clone the repo at that point.
