[Fix] Account Linking UpdateMigrationsByType (#31428)

Fix https://github.com/go-gitea/gitea/issues/31427

services/externalaccount/user.go

@@ -5,6 +5,7 @@ package externalaccount
 
 import (
 	"context"
+	"strconv"
 	"strings"
 
 	"code.gitea.io/gitea/models/auth"
@@ -82,6 +83,11 @@ func UpdateExternalUser(ctx context.Context, user *user_model.User, gothUser got
 
 // UpdateMigrationsByType updates all migrated repositories' posterid from gitServiceType to replace originalAuthorID to posterID
 func UpdateMigrationsByType(ctx context.Context, tp structs.GitServiceType, externalUserID string, userID int64) error {
+	// Skip update if externalUserID is not a valid numeric ID or exceeds int64
+	if _, err := strconv.ParseInt(externalUserID, 10, 64); err != nil {
+		return nil
+	}
+
 	if err := issues_model.UpdateIssuesMigrationsByType(ctx, tp, externalUserID, userID); err != nil {
 		return err
 	}