Automating keeping snmalloc up to date.

[Matthew Parkinson]

For Project Verona @plietar built a github action that automatically raises an issue if the snmalloc submodule is out of date. This might be useful for this project too:

https://github.com/microsoft/verona/blob/master/.github/workflows/update-snmalloc.yaml

[Outvi V]

Dependabot may have your back: https://dependabot.com/submodules/ .
A random PR sample: osyrisrblx/t#37

[Schrodinger ZHU Yifan]

I added a Dependabot to watch over the rust crates and git submodules at the same time.