🐛 `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