v2/internal/proxy: TestCheckConnections failed

[flaky-bot]

Note: #1884 was also for this test, but it was closed more than 10 days ago. So, I didn't mark it flaky.

---

commit: 54e65d1
buildURL: https://github.com/GoogleCloudPlatform/cloud-sql-proxy/actions/runs/8864322110
status: failed

[flaky-bot]

Looks like this issue is flaky. 😟

I'm going to leave this open and stop commenting.

A human should fix and close this.

---

When run at the same commit (54e65d1), this test passed in one build (https://github.com/GoogleCloudPlatform/cloud-sql-proxy/actions/runs/8864322110) and failed in another build (https://github.com/GoogleCloudPlatform/cloud-sql-proxy/actions/runs/8864322110).

[enocom]

=== RUN TestCheckConnections
2024/04/28 02:17:17 [proj:region:pg] Listening on 127.0.0.1:50000
2024/04/28 02:17:17 [proj:region:pg1] could not listen to address 127.0.0.1:60000: listen tcp 127.0.0.1:60000: bind: address already in use
proxy_test.go:669: proxy.NewClient error: [proj:region:pg1] Unable to mount socket: listen tcp 127.0.0.1:60000: bind: address already in use
--- FAIL: TestCheckConnections (0.00s)