Change migration graph to be compatible with backports

src/pretix/base/migrations/0162b_auto_20201218_1810.py

@@ -6,7 +6,7 @@ from django.db import migrations, models
 class Migration(migrations.Migration):
 
     dependencies = [
-        ('pretixbase', '0173_auto_20201211_1648'),
+        ('pretixbase', '0162_remove_seat_name'),
     ]
 
     operations = [

src/pretix/base/migrations/0174_merge_20201222_1031.py

@@ -0,0 +1,14 @@
+# Generated by Django 3.0.11 on 2020-12-22 10:31
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0173_auto_20201211_1648'),
+        ('pretixbase', '0162b_auto_20201218_1810'),
+    ]
+
+    operations = [
+    ]