Increase coverage for testing syntax highlighting

Created by: incident-io[bot]

A CI job that tests a large corpus of code and makes sure we can highlight it properly without timing out or crashing. This job could run periodically + optionally on request. We could create a fuzzing corpus based on errors we see in prod, and use those as seed values to fuzz the highlighter with the new fuzzing functionality in Go 1.18. Storyboard highlight test (of some example code with multi-byte, etc)

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This action was created from Incident 106 by dax, using incident.io 🔥