make creation date none changeable on save

InvenTree/common/migrations/0014_alter_notificationmessage_creation.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.2.5 on 2021-11-29 22:21
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('common', '0013_notificationmessage'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='notificationmessage',
+            name='creation',
+            field=models.DateTimeField(auto_now_add=True),
+        ),
+    ]