make the 'last_activity' field in /tickets show the actual last activity by making it a virtual field

core/tickets/migrations/0005_remove_issuethread_last_activity.py

@@ -0,0 +1,17 @@
+# Generated by Django 4.2.7 on 2024-01-10 19:04
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('tickets', '0004_remove_issuethread_state_alter_statechange_state'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='issuethread',
+            name='last_activity',
+        ),
+    ]