ProxyFilterIntegrationTest.DisableRefreshOnFailureContainsFailedHost is flaky

[adisuissa]

The test ProxyFilterIntegrationTest.DisableRefreshOnFailureContainsFailedHost defined in //test/extensions/filters/http/dynamic_forward_proxy:legacy_proxy_filter_integration_test seems to be flaky.

Full error when executed under compile-time-options build:

[ RUN      ] IpVersions/ProxyFilterIntegrationTest.DisableRefreshOnFailureContainsFailedHost/IPv4
test/extensions/filters/http/dynamic_forward_proxy/proxy_filter_integration_test.cc:573: Failure
Value of: response1->waitForEndStream()
  Actual: false (Timed out waiting for end stream
)
Expected: true
Stack trace:
  0x2bd402d: Envoy::(anonymous namespace)::ProxyFilterIntegrationTest_DisableRefreshOnFailureContainsFailedHost_Test::TestBody()
  0x6d501cb: testing::internal::HandleSehExceptionsInMethodIfSupported<>()
  0x6d403da: testing::internal::HandleExceptionsInMethodIfSupported<>()
  0x6d2c283: testing::Test::Run()
  0x6d2cc34: testing::TestInfo::Run()
... Google Test internal frames ...

test/integration/http_integration.cc:385: Failure
Expected equality of these values:
  codec_client_->numActiveRequests()
    Which is: 1
  0
test requires explicit cleanupUpstreamAndDownstream
Stack trace:
  0x2e539a0: Envoy::HttpIntegrationTest::~HttpIntegrationTest()
  0x2bc954b: Envoy::(anonymous namespace)::ProxyFilterIntegrationTest::~ProxyFilterIntegrationTest()
  0x2bd3aa5: Envoy::(anonymous namespace)::ProxyFilterIntegrationTest_DisableRefreshOnFailureContainsFailedHost_Test::~ProxyFilterIntegrationTest_DisableRefreshOnFailureContainsFailedHost_Test()
  0x2bd3ac9: Envoy::(anonymous namespace)::ProxyFilterIntegrationTest_DisableRefreshOnFailureContainsFailedHost_Test::~ProxyFilterIntegrationTest_DisableRefreshOnFailureContainsFailedHost_Test()
  0x6d40bb8: testing::Test::DeleteSelf_()
  0x6d501cb: testing::internal::HandleSehExceptionsInMethodIfSupported<>()
  0x6d403da: testing::internal::HandleExceptionsInMethodIfSupported<>()
  0x6d2cc7f: testing::TestInfo::Run()
  0x6d2d37b: testing::TestSuite::Run()
... Google Test internal frames ...

Link to failure: https://github.com/envoyproxy/envoy/actions/runs/13421390923/job/37494667336#step:17:4188

The test was introduced in #38215.
cc @fredyw