🐛 `TestLoadBalancerSuite/TestUpdateUpstreams` unit test is flaky

[utkuozdemir]

When run with -race:

#68 50.28 === NAME  TestLoadBalancerSuite/TestUpdateUpstreams
#68 50.28     logger.go:146: 2024-06-06T15:32:21.496Z   DEBUG   controller starting {"controller": "LoadBalancerController"}
#68 50.28     logger.go:146: 2024-06-06T15:32:21.496Z   DEBUG   starting loadbalancer   {"controller": "LoadBalancerController", "id": "", "port": 20000}
#68 50.28     loadbalancer_test.go:377: 
#68 50.28           Error Trace:    /src/internal/backend/runtime/omni/controllers/omni/loadbalancer_test.go:377
#68 50.28                                       /src/internal/backend/runtime/omni/controllers/omni/loadbalancer_test.go:393
#68 50.28           Error:          Not equal: 
#68 50.28                           expected: []string{"testEndpoint", "newEndpoint"}
#68 50.28                           actual  : []string{"testEndpoint"}
#68 50.28                           
#68 50.28                           Diff:
#68 50.28                           --- Expected
#68 50.28                           +++ Actual
#68 50.28                           @@ -1,4 +1,3 @@
#68 50.28                           -([]string) (len=2) {
#68 50.28                           - (string) (len=12) "testEndpoint",
#68 50.28                           - (string) (len=11) "newEndpoint"
#68 50.28                           +([]string) (len=1) {
#68 50.28                           + (string) (len=12) "testEndpoint"
#68 50.28                            }
#68 50.28           Test:           TestLoadBalancerSuite/TestUpdateUpstreams
#68 50.28     logger.go:146: 2024-06-06T15:32:21.497Z   DEBUG   controller finished {"controller": "LoadBalancerController"}
#68 50.28     omni_test.go:415: tear down

A failed run: https://github.com/siderolabs/omni/actions/runs/9403704984/job/25900871945