ref: ProjectCodeOwners.schema is never null (#84395)

this query returns no results in us or de:

```sql
select count(1) from sentry_projectcodeowners where schema is null;
```

<!-- Describe your PR here. -->

migrations_lockfile.txt

@@ -15,7 +15,7 @@ remote_subscriptions: 0003_drop_remote_subscription
 
 replays: 0004_index_together
 
-sentry: 0823_projectcodeowners_raw_never_null
+sentry: 0824_projectcodeowners_schema_non_null
 
 social_auth: 0002_default_auto_field
 

src/sentry/migrations/0824_projectcodeowners_schema_non_null.py

@@ -0,0 +1,34 @@
+# Generated by Django 5.1.5 on 2025-01-31 22:32
+
+from django.db import migrations
+
+import sentry.db.models.fields.jsonfield
+from sentry.new_migrations.migrations import CheckedMigration
+
+
+class Migration(CheckedMigration):
+    # This flag is used to mark that a migration shouldn't be automatically run in production.
+    # This should only be used for operations where it's safe to run the migration after your
+    # code has deployed. So this should not be used for most operations that alter the schema
+    # of a table.
+    # Here are some things that make sense to mark as post deployment:
+    # - Large data migrations. Typically we want these to be run manually so that they can be
+    #   monitored and not block the deploy for a long period of time while they run.
+    # - Adding indexes to large tables. Since this can take a long time, we'd generally prefer to
+    #   run this outside deployments so that we don't block them. Note that while adding an index
+    #   is a schema change, it's completely safe to run the operation after the code has deployed.
+    # Once deployed, run these manually via: https://develop.sentry.dev/database-migrations/#migration-deployment
+
+    is_post_deployment = True
+
+    dependencies = [
+        ("sentry", "0823_projectcodeowners_raw_never_null"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="projectcodeowners",
+            name="schema",
+            field=sentry.db.models.fields.jsonfield.JSONField(default=dict),
+        ),
+    ]

src/sentry/models/projectcodeowners.py

@@ -32,7 +32,7 @@ class ProjectCodeOwners(Model):
     # raw ⇒ original CODEOWNERS file.
     raw = models.TextField()
     # schema ⇒ transformed into IssueOwner syntax
-    schema = JSONField(null=True)
+    schema = JSONField()
     date_updated = models.DateTimeField(default=timezone.now)
     date_added = models.DateTimeField(default=timezone.now)