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

maybe more

services/asymkey/ssh_key_authorized_principals.go

@@ -122,6 +122,10 @@ func regeneratePrincipalKeys(ctx context.Context, t io.StringWriter) error {
 				return err
 			}
 		}
+		err = scanner.Err()
+		if err != nil {
+			return fmt.Errorf("scan: %w", err)
+		}
 		f.Close()
 	}
 	return nil

services/doctor/authorizedkeys.go

@@ -51,6 +51,10 @@ 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