Update database acceptance test fixture (#3665)

## Why

This field is now included in the response payload.

Author: pietern

acceptance/bundle/deploy/lakebase/database-instance/single-instance/output.txt

@@ -31,6 +31,7 @@ Deployment complete!
   "capacity": "CU_1",
   "creation_time": "[TIMESTAMP]Z",
   "creator": "[USERNAME]",
+  "effective_capacity": "CU_1",
   "effective_enable_pg_native_login": false,
   "effective_enable_readable_secondaries": false,
   "effective_node_count": 1,

libs/testserver/database_instances.go

@@ -34,6 +34,7 @@ func (s *FakeWorkspace) DatabaseInstanceCreate(req Request) Response {
 	databaseInstance.PgVersion = "PG_VERSION_16"
 	databaseInstance.EffectiveNodeCount = 1
 	databaseInstance.EffectiveRetentionWindowInDays = 7
+	databaseInstance.EffectiveCapacity = databaseInstance.Capacity
 	databaseInstance.Creator = req.Workspace.CurrentUser().UserName
 	databaseInstance.CreationTime = time.Now().UTC().Format(time.RFC3339)
 	databaseInstance.EffectiveEnableReadableSecondaries = false