Fix GitHub translation key category (#3926)

## Description:

The GitHub translation key was incorrectly categorized under news even
though it is used on the main page.
This changes its category to main.

## Please complete the following:

- [ ] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

aotumuri

src/client/components/Footer.ts

@@ -24,7 +24,7 @@ export class Footer extends LitElement {
           >
             <img
               src=${assetUrl("icons/github-mark-white.svg")}
-              data-i18n-alt="news.github_link"
+              data-i18n-alt="main.github"
               class="h-6 w-6 lg:h-7 lg:w-7 object-contain pointer-events-none"
               draggable="false"
             />