Simplify query to find existing alert

What does this MR do and why?

There is a unique index for non-resolved alerts on project_id & fingerprint. When processing new alert notifications, we check for an existing alert record with a matching fingerprint first. This query currently has an ORDER BY clause, but as there can only be one matching record (or none), the ordering does not need to be present.

Related issue: https://gitlab.com/gitlab-org/gitlab/-/issues/348676

Before

SELECT "alert_management_alerts".* FROM "alert_management_alerts"
WHERE ("alert_management_alerts"."status" NOT IN (2)) 
  AND "alert_management_alerts"."project_id" = <PROJECT_ID>
  AND "alert_management_alerts"."fingerprint" = <FINGERPRINT>
ORDER BY "alert_management_alerts"."id" ASC 
LIMIT 1

 Limit  (cost=2.17..2.18 rows=1 width=67) (actual time=1.124..1.125 rows=1 loops=1)
   ->  Sort  (cost=2.17..2.18 rows=1 width=67) (actual time=1.124..1.124 rows=1 loops=1)
         Sort Key: id
         Sort Method: quicksort  Memory: 25kB
         ->  Index Scan using index_partial_am_alerts_on_project_id_and_fingerprint on alert_management_alerts  (cost=0.14..2.16 rows=1 width=67) (actual time=1.112..1.114 rows=1 loops=1)
               Index Cond: ((project_id = 21) AND (fingerprint = '\x6d22d10d758340a970007528918fb69f2e14b2a0'::bytea))
 Planning Time: 0.132 ms
 Execution Time: 1.143 ms
(8 rows)

After

SELECT "alert_management_alerts".* FROM "alert_management_alerts" 
WHERE "alert_management_alerts"."project_id" = <PROJECT_ID> 
  AND "alert_management_alerts"."fingerprint" = <FINGERPRINT>
  AND ("alert_management_alerts"."status" NOT IN (2)) 
LIMIT 1

 Limit  (cost=0.14..2.16 rows=1 width=67) (actual time=0.012..0.013 rows=1 loops=1)
   ->  Index Scan using index_partial_am_alerts_on_project_id_and_fingerprint on alert_management_alerts  (cost=0.14..2.16 rows=1 width=67) (actual time=0.012..0.012 rows=1 loops=1)
         Index Cond: ((project_id = 21) AND (fingerprint = '\x6d22d10d758340a970007528918fb69f2e14b2a0'::bytea))
 Planning Time: 0.117 ms
 Execution Time: 0.026 ms
(5 rows)

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