chore(github): log result when no default branch returned

lib/modules/platform/github/index.ts

@@ -512,6 +512,10 @@ export async function initRepo({
     }
     // istanbul ignore if
     if (!repo.defaultBranchRef?.name) {
+      logger.debug(
+        { res },
+        'No default branch returned - treating repo as empty',
+      );
       throw new Error(REPOSITORY_EMPTY);
     }
     if (