In response to ongoing [github actions incident](https://www.githubstatus.com/incidents/c7kq3ctclddp) Supercedes: https://github.com/zed-industries/zed/pull/36698 Release Notes: - N/A
Fixes shellcheck errors in script/* Adds a couple trailing newlines. Adds `script/shellcheck-scripts` and associated CI machinery. Current set ultra-conservative, does not output warnings, only errors.