ccl/sqlproxyccl: TestPrivateEndpointsACL failed

ccl/sqlproxyccl.TestPrivateEndpointsACL [failed](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Ci_TestsAwsLinuxArm64_UnitTests/21332028?buildTab=log) with [artifacts](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Ci_TestsAwsLinuxArm64_UnitTests/21332028?buildTab=artifacts#/) on release-25.4 @ [1ab2d1a5747a80ea24d279f8a241441533787659](https://github.com/cockroachdb/cockroach/commits/1ab2d1a5747a80ea24d279f8a241441533787659):

```
=== RUN TestPrivateEndpointsACL
test_log_scope.go:171: test logs captured to: /artifacts/tmp/_tmp/8b67916b40b2ca2b9d724d711ff9c3e7/logTestPrivateEndpointsACL2786812697
test_log_scope.go:82: use -show-logs to present logs inline
proxy_handler_test.go:471: -- test log scope end --
test logs left over in: /artifacts/tmp/_tmp/8b67916b40b2ca2b9d724d711ff9c3e7/logTestPrivateEndpointsACL2786812697
--- FAIL: TestPrivateEndpointsACL (4.22s)
=== RUN TestPrivateEndpointsACL/private_connection_allowed
proxy_handler_test.go:400:
Error Trace: pkg/ccl/sqlproxyccl/proxy_handler_test.go:2950
Error: Expected nil, but got: &sqlproxyccl.errWithCode{
code: 4,
cause: &withstack.withStack{
cause: &errutil.withPrefix{
cause: &errors.errorString{s:"proxyproto: proxy protocol signature not present"},
prefix: "while receiving startup message",
},
stack: &withstack.stack{0x48a1c11, 0x48ae28c, 0x48b3e40, 0x18d0be8, 0x493994},
},
}
Test: TestPrivateEndpointsACL/private_connection_allowed
--- FAIL: TestPrivateEndpointsACL/private_connection_allowed (0.04s)
```
Help

See also: [How To Investigate a Go Test Failure \(internal\)](https://cockroachlabs.atlassian.net/l/c/HgfXfJgM)

Same failure on other branches

- #148597 ccl/sqlproxyccl: TestPrivateEndpointsACL failed [C-test-failure O-robot T-cloud-platform branch-release-24.3.15-rc release-blocker]
- #136387 ccl/sqlproxyccl: TestPrivateEndpointsACL failed [C-test-failure O-robot T-cloud-platform branch-release-24.3]

/cc @cockroachdb/sqlproxy-prs

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Jira issue: CRDB-63407