Mark migrations with data operations "non atomic"

Ref: https://docs.djangoproject.com/en/dev/howto/writing-migrations/#non-atomic-migrations

InvenTree/part/migrations/0020_auto_20190908_0404.py

@@ -12,6 +12,8 @@ def update_tree(apps, schema_editor):
 
 class Migration(migrations.Migration):
 
+    atomic = False
+
     dependencies = [
         ('part', '0019_auto_20190908_0404'),
     ]

InvenTree/part/migrations/0034_auto_20200404_1238.py

@@ -18,6 +18,8 @@ def create_thumbnails(apps, schema_editor):
 
 class Migration(migrations.Migration):
 
+    atomic = False
+
     dependencies = [
         ('part', '0033_auto_20200404_0445'),
     ]

InvenTree/part/migrations/0039_auto_20200515_1127.py

@@ -16,6 +16,8 @@ def nupdate_tree(apps, schema_editor):
 
 class Migration(migrations.Migration):
 
+    atomic = False
+
     dependencies = [
         ('part', '0038_auto_20200513_0016'),
     ]

InvenTree/part/migrations/0056_auto_20201110_1125.py

@@ -138,6 +138,8 @@ def reverse_currencies(apps, schema_editor):
 
 class Migration(migrations.Migration):
 
+    atomic = False
+
     dependencies = [
         ('part', '0055_auto_20201110_1001'),
     ]