Fix issue label delete incorrect labels webhook payload (#34575)

Fixes https://github.com/go-gitea/gitea/issues/34560
explanation of the bug in the issue

setting `issue.isLabelsLoaded = false` before calling `deleteIssueLabel`
guarantee we will load the new state of the labels into the issue object
before sending it in the webhook.

models/issues/issue_label.go

@@ -206,6 +206,7 @@ func DeleteIssueLabel(ctx context.Context, issue *Issue, label *Label, doer *use
 	}
 
 	issue.Labels = nil
+	issue.isLabelsLoaded = false
 	return issue.LoadLabels(ctx)
 }