Suppress `ExternalLoginUserNotExist` error (#21504) (#21572)

Backport of #21504

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/web/auth/auth.go

@@ -613,7 +613,9 @@ func handleUserCreated(ctx *context.Context, u *user_model.User, gothUser *goth.
 	// update external user information
 	if gothUser != nil {
 		if err := externalaccount.UpdateExternalUser(u, *gothUser); err != nil {
-			log.Error("UpdateExternalUser failed: %v", err)
+			if !user_model.IsErrExternalLoginUserNotExist(err) {
+				log.Error("UpdateExternalUser failed: %v", err)
+			}
 		}
 	}
 

routers/web/auth/oauth.go

@@ -1061,7 +1061,9 @@ func handleOAuth2SignIn(ctx *context.Context, source *auth.Source, u *user_model
 
 		// update external user information
 		if err := externalaccount.UpdateExternalUser(u, gothUser); err != nil {
-			log.Error("UpdateExternalUser failed: %v", err)
+			if !user_model.IsErrExternalLoginUserNotExist(err) {
+				log.Error("UpdateExternalUser failed: %v", err)
+			}
 		}
 
 		if err := resetLocale(ctx, u); err != nil {