QuicHttpIntegrationTests/QuicHttpIntegrationTest.Http3ClientKeepalive is flaky

[adisuissa]

full details here:

[ RUN      ] QuicHttpIntegrationTests/QuicHttpIntegrationTest.Http3ClientKeepalive/IPv4
test/integration/quic_http_integration_test.cc:1092: Failure
Expected: (quic_connection_->GetStats().ping_frames_sent) <= (8u), actual: 9 vs 8
Stack trace:
  0xbd5931: Envoy::Quic::QuicHttpIntegrationTest_Http3ClientKeepalive_Test::TestBody()
  0x2114aac: testing::internal::HandleExceptionsInMethodIfSupported<>()
  0x211496d: testing::Test::Run()
  0x2115c67: testing::TestInfo::Run()
... Google Test internal frames ...

cc @danzh2010