Optimize and improve test coverage for cli/src/config (#13485)

packages/cli/src/config/extensions/github.ts

@@ -457,7 +457,7 @@ export function findReleaseAsset(assets: Asset[]): Asset | undefined {
   return undefined;
 }
 
-async function downloadFile(url: string, dest: string): Promise<void> {
+export async function downloadFile(url: string, dest: string): Promise<void> {
   const headers: {
     'User-agent': string;
     Accept: string;