sp_Blitz: skip AG/cluster and master.sys.master_files checks on Azure SQL DB

Second round of Copilot review on BrentOzarULTD#3951 flagged three more CheckIDs
that will error on Azure SQL Database:

- CheckID 53 (Cluster Node) - queries sys.dm_hadr_availability_replica_
  cluster_states and SERVERPROPERTY('IsHadrEnabled'/'IsClustered'), none
  of which are available on Azure SQL DB.
- CheckID 234 (SQL Server Update May Fail) - queries master.sys.master_files
  via three-part name.
- CheckID 268 (AG Replica Falling Behind) - queries
  sys.dm_hadr_database_replica_states, sys.availability_replicas, and
  sys.availability_groups, none of which exist on Azure SQL DB.

Also broadened the section comment from "Replication / mirroring / AGs" to
include "clustering" to match the expanded list.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: BrentOzar

sp_Blitz.sql

@@ -997,8 +997,11 @@ BEGIN
 						INSERT INTO #SkipChecks (CheckID) VALUES (260); /* SQL Server service account in Administrators */
 						INSERT INTO #SkipChecks (CheckID) VALUES (261); /* Agent service account in Administrators */
 
-						/* Replication / mirroring / AGs - not applicable on Azure SQL DB */
+						/* Replication / mirroring / AGs / clustering - not applicable on Azure SQL DB */
+						INSERT INTO #SkipChecks (CheckID) VALUES (53);  /* Cluster Node - sys.dm_hadr_* DMVs unavailable */
 						INSERT INTO #SkipChecks (CheckID) VALUES (227); /* Database Mirroring */
+						INSERT INTO #SkipChecks (CheckID) VALUES (234); /* SQL Server Update May Fail - queries master.sys.master_files */
+						INSERT INTO #SkipChecks (CheckID) VALUES (268); /* AG Replica Falling Behind - sys.availability_* DMVs unavailable */
 
 			            INSERT  INTO #BlitzResults
 			            ( CheckID ,