test: increases a test timeout to avoid flaky failures

[birenroy]

In my repro attempts, I saw failures with both the nghttp2 and oghttp2 codecs.

Addresses the bulk of the failures from #32132.

Tested via:

$ baze test --config=clang-tsan --config=remote test/integration:multiplexed_integration_test \
  --runs_per_test=1000 --test_filter='IpVersions/Http2FrameIntegrationTest.CloseConnectionWithDeferredStreams/*' \
  --test_sharding_strategy=disabled

With the timeout extension, I saw 1 failure in 1000 runs, which is significantly better than before.

Commit Message: Increases a test timeout to avoid flaky failures
Additional Description:
Risk Level: none, tests only
Testing: ran 1000 iterations of the suspicious test case
Docs Changes:
Release Notes:
Platform Specific Features:

[repokitteh-read-only]

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🐱

Caused by: #32232 was opened by birenroy.

see: more, trace.

[birenroy]

/assign @RyanTheOptimist
/assign @phlax

[RyanTheOptimist]

Thanks for doing this, Biren!