//test/extensions/filters/http/dynamic_forward_proxy:proxy_filter_integration_test is flaky

[antoniovleonti]

[ RUN      ] IpVersions/ProxyFilterIntegrationTest.SubClusterWithUnknownDomain/IPv6
test/extensions/filters/http/dynamic_forward_proxy/proxy_filter_integration_test.cc:1182: Failure
Value of: waitForAccessLog(access_log_name_)
Expected: has substring "no_healthy_upstream"
  Actual: "sub_cluster_warming_timeout"
Stack trace:
  0x5504b0f: Envoy::(anonymous namespace)::ProxyFilterIntegrationTest_SubClusterWithUnknownDomain_Test::TestBody()
  0xf1838d5: testing::internal::HandleExceptionsInMethodIfSupported<>()
  0xf14b603: testing::Test::Run()
  0xf14d178: testing::TestInfo::Run()
... Google Test internal frames ...

test/extensions/filters/http/dynamic_forward_proxy/proxy_filter_integration_test.cc:1187: Failure
Value of: waitForAccessLog(access_log_name_, 1)
Expected: has substring "no_healthy_upstream"
  Actual: "sub_cluster_warming_timeout"
Stack trace:
  0x5505386: Envoy::(anonymous namespace)::ProxyFilterIntegrationTest_SubClusterWithUnknownDomain_Test::TestBody()
  0xf1838d5: testing::internal::HandleExceptionsInMethodIfSupported<>()
  0xf14b603: testing::Test::Run()
  0xf14d178: testing::TestInfo::Run()
... Google Test internal frames ...

[external/com_google_absl/absl/flags/internal/flag.cc : 115] RAW: Restore saved value of envoy_quic_always_support_server_preferred_address to: true
[external/com_google_absl/absl/flags/internal/flag.cc : 115] RAW: Restore saved value of envoy_reloadable_features_no_extension_lookup_by_name to: true
[external/com_google_absl/absl/flags/internal/flag.cc : 115] RAW: Restore saved value of envoy_reloadable_features_runtime_initialized to: false
[  FAILED  ] IpVersions/ProxyFilterIntegrationTest.SubClusterWithUnknownDomain/IPv6, where GetParam() = 4-byte object <01-00 00-00> (10435 ms)

https://dev.azure.com/cncf/envoy/_build/results?buildId=179725&view=logs&j=1439b9f7-a348-5b50-b5fe-ea612ea91241&t=1002ac43-da84-5fae-70b2-98833b702d09

Seen in CI for #35698