`TestAgentSmoothedRTT` flakiness

[ravicious]

Failure

Link(s) to logs

• https://github.com/gravitational/teleport/actions/runs/27751758169/job/82103694436#step:6:3234

Relevant snippet

    agent_test.go:420: 
        	Error Trace:	/__w/teleport/teleport/lib/reversetunnel/agent_test.go:420
        	Error:      	Not equal: 
        	            	expected: 30ms
        	            	actual  : 20ms
        	Test:       	TestAgentSmoothedRTT