change healthcheck from `github.com` to `raw.githubusercontent.com`

[michelonfelipe]

Why

Recently, when installing decky, plugin_loader-${BRANCH}.service had the content of 429 response from github, instead of the expected content This happened because the healthcheck from the beginning of the file only checks for github.com access (which is not actually used), and do not checks for raw.githubusercontent.com

There was actually a wide problem on south america accessing raw.githubusercontent.com. More info in an community discussion

What

Change healthcheck from github.com to raw.githubusercontent.com The default status code is 301, because the homepage redirects to github.com