xdsclient: Fix flakyness in TestResourceUpdateMetrics in the case of repeated NACKs#8363

purnesh42H merged 2 commits intogrpc:mastergrpc/grpc-go:masterfrom

purnesh42H:xds-remove-unexpected-test-timeoutpurnesh42H/grpc-go:xds-remove-unexpected-test-timeoutCopy head branch name to clipboard