Github Actions CI to reduce to_sandbox and to_production bugs

I fixed a typo bug recently introduced into `/to_sandbox.txt` (https://github.com/google/fonts/commit/d40de44891816dd5b952c2b1231b9d88bca357b2)

I wonder if we can have a very simple Github Actions CI script that

- [ ] sorts the contents of the files, compares the output to the input, and if there is a diff, FAILs

- [x] checks that the path exists, and if not, FAILs

Getting fancy, I can imagine these checks could auto-fix...

- [ ] sort can auto commit and push to master the sorted version
- [ ] if a paths exists with the same characters just reordered (as in the above typo) then replace the path not found with the path available and make a PR