ref: have AlertRule.detection_type code match schema width (#91898)

the migration which added this column added it as varchar(32) but this
was not reflected in code until now -- fix it with a state-only
migration

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

Author: asottile-sentry

migrations_lockfile.txt

@@ -21,7 +21,7 @@ remote_subscriptions: 0003_drop_remote_subscription
 
 replays: 0005_drop_replay_index
 
-sentry: 0901_org_slug_wrong_index_name
+sentry: 0902_detection_type_match_size
 
 social_auth: 0002_default_auto_field
 

src/sentry/incidents/models/alert_rule.py

@@ -220,6 +220,7 @@ class AlertRule(Model):
     )
     description = models.CharField(max_length=1000, null=True)
     detection_type = models.CharField(
+        max_length=32,
         default=AlertRuleDetectionType.STATIC,
         db_default=AlertRuleDetectionType.STATIC,
         choices=AlertRuleDetectionType.choices,

src/sentry/migrations/0902_detection_type_match_size.py

@@ -0,0 +1,37 @@
+# Generated by Django 5.2.1 on 2025-05-19 20:54
+
+from django.db import migrations, models
+
+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 = False
+
+    dependencies = [
+        ("sentry", "0901_org_slug_wrong_index_name"),
+    ]
+
+    operations = [
+        migrations.SeparateDatabaseAndState(
+            state_operations=[
+                migrations.AlterField(
+                    model_name="alertrule",
+                    name="detection_type",
+                    field=models.CharField(db_default="static", default="static", max_length=32),
+                ),
+            ]
+        ),
+    ]