report early if we dont have github data set up

lib/upload.js

@@ -14,6 +14,10 @@ function isBrokenBuild (nodeVersion, targetArch) {
 }
 
 export async function main () {
+  if (!process.env.GITHUB_USERNAME) {
+    throw new Error('No github credentials. Upload will fail!');
+  }
+
   for (const nodeVersion in patchesJson) {
     for (const targetArch of targetArchs) {
       if (isBrokenBuild(nodeVersion, targetArch)) continue;