`TestListUnifiedInstances` flakiness

[rosstimothy]

Failure

Link(s) to logs

• https://github.com/gravitational/teleport/actions/runs/31424268298/job/93572133990?pr=69479

Relevant snippet

    inventory_test.go:185: 
        	Error Trace:	/__w/teleport/teleport/lib/web/inventory_test.go:191
        	            				/opt/go/src/runtime/asm_amd64.s:1771
        	Error:      	"[{bot-1 bot_instance <nil> 0xc025ee5640} {bot-2 bot_instance <nil> 0xc025ee56a0} {bot-3 bot_instance <nil> 0xc025ee56c0} {instance-1 instance 0xc001a670c0 <nil>} {instance-2 instance 0xc001a67100 <nil>} {instance-3 instance 0xc001a67140 <nil>} {instance-4 instance 0xc001a67180 <nil>} {instance-5 instance 0xc001a671c0 <nil>} {instance-6 instance 0xc001a67240 <nil>} {node instance 0xc001a67280 <nil>}]" should have 9 item(s), but has 10
        	Messages:   	should have 9 items (6 instances + 3 bots)
    inventory_test.go:185: 
        	Error Trace:	/__w/teleport/teleport/lib/web/inventory_test.go:185
        	Error:      	Condition never satisfied
        	Test:       	TestListUnifiedInstances
        	Messages:   	inventory cache failed to become healthy and populated