Add CI fuzzing

[johanbrandhorst]

Fixes #432

[jhump]

@johanbrandhorst, neat! Do I need to do anything with repo config for this to work? Where would I see the checks? Should they show up above, like alongside the "Circle CI" checks?

[johanbrandhorst]

They show up in the CI checks like the circleCI jobs. I'm surprised this PR hasn't triggered one tbh, do you need to enable github actions on the repository? You can see what happened on the grpc-gateway PR: grpc-ecosystem/grpc-gateway#2405 (it created a Fuzzing job on the PR).

Re: #432 (comment), if the parser is already fuzzed continuously, then the value of this PR diminishes. It might be able to find crashers in new code sooner, but it also means every CI run takes 600 seconds to finish. Up to you what you want to do :).

[WillAbides]

I'm surprised this PR hasn't triggered one

I think this hasn't triggered because PRs from people other than the owner don't trigger actions in order to prevent people from running malicious code through pull requests. It's documented here: https://docs.github.com/en/actions/managing-workflow-runs/approving-workflow-runs-from-public-forks