fix(aci): Gracefully handle missing OrganizationMember in MetricAlert target lookup

[jasonyuezhang]

If there is no org member associated with this user and organization, then we should exit gracefully.

---

Copied from getsentry#102113
Original PR: getsentry#102113

[propel-test-bot]

Gracefully handle missing OrganizationMember in metric alert notification target resolution

Adds a try/except OrganizationMember.DoesNotExist block around the lookup of the user-org relation when resolving a notification action target. If the user is no longer in the organization, the handler now returns None instead of raising, avoiding workflow crashes.

Key Changes

• Wrapped OrganizationMember.objects.get in a try/except OrganizationMember.DoesNotExist block
• Added inline comment explaining why the exception is ignored

Affected Areas

• src/sentry/notifications/notification_action/group_type_notification_registry/handlers/metric_alert_registry_handler.py

This summary was automatically generated by @propel-code-bot

[propel-test-bot]

[BestPractice]

The function now exits gracefully when OrganizationMember doesn't exist, but it doesn't return None explicitly. While Python functions return None by default, it's clearer to be explicit about the return value when handling the exception case.

Suggested change

	except OrganizationMember.DoesNotExist:
	# user is no longer a member of the organization
	pass
	except OrganizationMember.DoesNotExist:
	# user is no longer a member of the organization
	return None

⚡ Committable suggestion

Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation.

Context for Agents

[**BestPractice**]

The function now exits gracefully when OrganizationMember doesn't exist, but it doesn't return None explicitly. While Python functions return None by default, it's clearer to be explicit about the return value when handling the exception case.

```suggestion
            except OrganizationMember.DoesNotExist:
                # user is no longer a member of the organization
                return None
```

⚡ **Committable suggestion**

Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation.

File: src/sentry/notifications/notification_action/group_type_notification_registry/handlers/metric_alert_registry_handler.py
Line: 56