fix: Have the URL be the project URL itself

(I think, doesn't seem to work for the waffle though, probably because
of the staging API :/)

launcher/modplatform/modrinth/ModrinthPackManifest.h

@@ -39,6 +39,7 @@ struct File
 struct ModpackExtra {
     QString body;
 
+    QString projectUrl;
     QString sourceUrl;
     QString wikiUrl;
 };