Transient transport error test failures in otap-dataflow

[drewrelmas]

We've seen a few unrelated PRs get kicked from the merge queue due to failing test in otap-dataflow.

FAIL [   0.015s] otap-df-otap otap_exporter::tests::test_otap_exporter

running 1 test
test otap_exporter::tests::test_otap_exporter ... FAILED

failures:
    otap_exporter::tests::test_otap_exporter

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 26 filtered out; finished in 0.00s

thread 'otap_exporter::tests::test_otap_exporter' panicked at /home/runner/work/otel-arrow/otel-arrow/rust/otap-dataflow/crates/engine/src/testing/exporter.rs:223:18:
Exporter event loop failed: ExporterError { exporter: "test_exporter", error: "transport error" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

thread 'otap_exporter::tests::test_otap_exporter' panicked at /home/runner/work/otel-arrow/otel-arrow/rust/otap-dataflow/crates/engine/src/testing/exporter.rs:298:14:
Exporter task failed: JoinError::Panic(Id(6), "Exporter event loop failed: ExporterError { exporter: \"test_exporter\", error: \"transport error\" }", ...)