[Durability]: SyncWrite update incrementing the cbstats' vb-details:ops_update field by 2

Build: 6.5.0-4558.

Scenario:

• 4 node cluster, Couchbase-bucket (replica=0)
• Insert 2 docs with durability=MAJORITY
• Update 1 doc with durability=MAJORITY
  ops_update count is 2 after step#2
  cbstats vbucket-details stats with replica=0. (Replica number doesn't matter here). We are getting same result with all replica values

Cbstats output values:

ops_create for default: 2
ops_delete for default: 0
ops_update for default: 2
ops_reject for default: 0
ops_get for default: 1
rollback_item_count for default: 0
sync_write_aborted_count for default: 0
sync_write_committed_count for default: 3
pending_writes for default: 0

Error: Mismatch in ops_update stats. 2 != 1

TAF test:

epengine.basic_ops.basic_ops.test_doc_size.nodes_init=4,num_items=2,doc_size=1024,doc_op=update,replicas=0,durability=MAJORITY

Note: This is similar to MB-34672