Make nightly build test against updated dependencies

[Nemo157]

#122 should have been picked up automatically when zstd 0.8.2 was released; there should be another job that runs nightly (but using the stable compiler), updates all dependencies, then runs the tests, and opens an issue if there is a failure.

[Xuanwo]

there should be another job that runs nightly (but using the stable compiler), updates all dependencies, then runs the tests, and opens an issue if there is a failure.

Maybe we can use dependabot.

[robjtede]

at some point stopped tracking the lockfile, so nightly job runs will catch these issues now