During dev when fetching data locally, check repo SHA

To get the latest commit of a distant repo:
"https://api.github.com/repos/devographics/surveys/commits/main"
(see https://stackoverflow.com/questions/45726013/how-can-i-get-last-commit-from-github-api)

To get the latest commit of a local repo:
```
git rev-parse HEAD
```
(see https://stackoverflow.com/questions/949314/how-do-i-get-the-hash-for-the-current-commit-in-git)

It should probably throw in dev, and warn in prod.