Fixed #24529 -- Allowed double squashing of migrations.

Co-authored-by: Raphael Gaschignard <raphael@rtpg.co>

tests/migrations/test_migrations_squashed_loop/2_squashed.py

@@ -0,0 +1,7 @@
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+    replaces = [("migrations", "2_auto")]
+    dependencies = [("migrations", "1_auto")]
+    operations = [migrations.RunPython(migrations.RunPython.noop)]