ExtProcIntegrationTest.GetAndSetTrailersIncorrectlyOnResponse is flakey

[phlax]

this is failing fairly regularly

[ RUN      ] IpVersionsClientTypeDeferredProcessing/ExtProcIntegrationTest.GetAndSetTrailersIncorrectlyOnResponse/IPv4_GoogleGrpc_NoDeferredProcessing
test/extensions/filters/http/ext_proc/ext_proc_integration_test.cc:257: Failure
Value of: response.waitForEndStream()
  Actual: false (Timed out waiting for end stream
)
Expected: true
Stack trace:
  0xc93382: Envoy::ExtProcIntegrationTest::verifyDownstreamResponse()
  0xca96c4: Envoy::ExtProcIntegrationTest_GetAndSetTrailersIncorrectlyOnResponse_Test::TestBody()
  0x23f3bec: testing::internal::HandleExceptionsInMethodIfSupported<>()
  0x23f3aad: testing::Test::Run()
  0x23f4da7: testing::TestInfo::Run()
... Google Test internal frames ...

https://dev.azure.com/cncf/envoy/_build/results?buildId=170033&view=logs&j=8c169225-0ae8-53bd-947f-07cb81846cb5&t=d1a98671-b7ba-5fbf-f06c-ff337c010df4&l=3408

afaict it has been failing since ~22nd April

most likely todays fail was triggered by cache getting busted by #33830

[phlax]

cc @yanjunxiang-google

[yanjunxiang-google]

This is another timer related flakiness similar to #33017 . Let's tackle them together there.