Fix flaky cluster.Registry test.

[jmalloc]

Running make test-until-failure eventually results in:

    --- FAIL: TestRegistry/it_observes_registration_and_deregistration (0.26s)
        registry_test.go:59: start the observer before the registrar
        registry_test.go:63: running "observer" in the background background until the test ends
        registry_test.go:65: wait several poll intervals to ensure that the observer is running
        registry_test.go:67: 150ms elapsed without receiving a value on the channel, as expected
        registry_test.go:73: start the registrar and await notification of registration
        registry_test.go:77: running "registrar" to completion in the background before the test ends
        spruce.go:73: [DEBUG] cluster node registered
            ├── node_id ┈┈┈┈┈┈┈┈ 90971473-c608-45cc-acf6-9a19af45d8e3
            ├── addresses ┈┈┈┈┈┈ "10.0.0.1:50555, 129.168.0.1:50555"
            ├── expires_at ┈┈┈┈┈ "2024-03-17 15:52:51.458565 +1000 AEST"
            ╰── renew_interval ┈ 10ms
        spruce.go:73: [DEBUG] cluster node registration renewed
            ├── node_id ┈┈┈┈┈┈┈┈ 90971473-c608-45cc-acf6-9a19af45d8e3
            ├── expires_at ┈┈┈┈┈ "2024-03-17 15:52:51.468786 +1000 AEST"
            ╰── renew_interval ┈ 10ms
        spruce.go:73: [DEBUG] cluster node registration renewed
            ├── node_id ┈┈┈┈┈┈┈┈ 90971473-c608-45cc-acf6-9a19af45d8e3
            ├── expires_at ┈┈┈┈┈ "2024-03-17 15:52:51.47967 +1000 AEST"
            ╰── renew_interval ┈ 10ms
        spruce.go:73: [DEBUG] cluster node registration renewed
            ├── node_id ┈┈┈┈┈┈┈┈ 90971473-c608-45cc-acf6-9a19af45d8e3
            ├── expires_at ┈┈┈┈┈ "2024-03-17 15:52:51.489719 +1000 AEST"
            ╰── renew_interval ┈ 10ms
        spruce.go:73: [DEBUG] cluster node registration renewed
            ├── node_id ┈┈┈┈┈┈┈┈ 90971473-c608-45cc-acf6-9a19af45d8e3
            ├── expires_at ┈┈┈┈┈ "2024-03-17 15:52:51.499452 +1000 AEST"
            ╰── renew_interval ┈ 10ms
        spruce.go:73: [DEBUG] cluster node registration renewed
            ├── node_id ┈┈┈┈┈┈┈┈ 90971473-c608-45cc-acf6-9a19af45d8e3
            ├── expires_at ┈┈┈┈┈ "2024-03-17 15:52:51.508626 +1000 AEST"
            ╰── renew_interval ┈ 10ms
        registry_test.go:80: received the expected value on the channel
        registry_test.go:90: wait several renew/poll intervals to ensure that the node's registration is renewed properly
        spruce.go:73: [DEBUG] cluster node registration renewed
            ├── node_id ┈┈┈┈┈┈┈┈ 90971473-c608-45cc-acf6-9a19af45d8e3
            ├── expires_at ┈┈┈┈┈ "2024-03-17 15:52:51.522544 +1000 AEST"
            ╰── renew_interval ┈ 10ms
        asm_arm64.s:1222: "registrar" returned an error: cluster node registration expired
        registry_test.go:93: channel received a value while expecting channel to block
        registry_test.go:93:   cluster.MembershipChanged{
              	Registered:   nil,
            - 	Deregistered: nil,
            + 	Deregistered: []cluster.Node{
            + 		{
            + 			ID:        s"upper:10418818750421157324 lower:12463318453899876579",
            + 			Addresses: []string{"10.0.0.1:50555", "129.168.0.1:50555"},
            + 		},
            + 	},
              }
            
        registry_test.go:77: "registrar" returned an error, expected it to return successfully: cluster node registration expired