Fix missing error check of bufio.Scanner (#29882)

maybe more

(cherry picked from commit 0e183d81fc5283f9d2047472de580e4f04a046c1)

services/doctor/authorizedkeys.go

@@ -50,6 +50,10 @@ func checkAuthorizedKeys(ctx context.Context, logger log.Logger, autofix bool) e
 		}
 		linesInAuthorizedKeys.Add(line)
 	}
+	err = scanner.Err()
+	if err != nil {
+		return fmt.Errorf("scan: %w", err)
+	}
 	f.Close()
 
 	// now we regenerate and check if there are any lines missing