Fix /api/tasks leads to 500 server error

CHANGELOG.md

@@ -63,6 +63,7 @@ Tracks can be exported/imported to/from Datumaro and Sly Pointcloud formats (<ht
 - Clean up disk space after a project is removed (<https://github.com/opencv/cvat/pull/5632>)
 - \[Server API\] Various errors in the generated schema (<https://github.com/opencv/cvat/pull/5575>)
 - SiamMask and TransT serverless functions (<https://github.com/opencv/cvat/pull/5658>)
+- Сreating a project with the same labels and re-deleting of skeleton sublabels (<https://github.com/opencv/cvat/pull/5700>)
 
 ### Security
 - Fixed vulnerability with social authentication (<https://github.com/opencv/cvat/pull/5521>)

cvat/apps/engine/migrations/0063_alter_label_unique_together.py

@@ -0,0 +1,17 @@
+# Generated by Django 3.2.17 on 2023-02-15 14:39
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('engine', '0062_delete_previews'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='label',
+            unique_together={('task', 'name', 'parent'), ('project', 'name', 'parent')},
+        ),
+    ]

cvat/apps/engine/models.py

@@ -521,7 +521,8 @@ def has_parent_label(self):
 
     class Meta:
         default_permissions = ()
-        unique_together = ('task', 'name', 'parent')
+        unique_together = (('task', 'name', 'parent'),
+                           ('project', 'name', 'parent'))
 
 class Skeleton(models.Model):
     root = models.OneToOneField(Label, on_delete=models.CASCADE)