Test flake from #8299

[jack-berg]

#8299 introduce a new test which is flaky. Example:

[43](https://github.com/open-telemetry/opentelemetry-java/actions/runs/24581486461/job/71880205316#step:6:1944)
PeriodicMetricReaderTest > shutdown_whileExportInFlight_waitsThenPerformsFinalExport() FAILED
    org.opentest4j.AssertionFailedError: 
    expected: 2
     but was: 1
        at app//io.opentelemetry.sdk.metrics.export.PeriodicMetricReaderTest.shutdown_whileExportInFlight_waitsThenPerformsFinalExport(PeriodicMetricReaderTest.java:314)

PeriodicMetricReaderTest > shutdown_whileExportInFlight_waitsThenPerformsFinalExport() FAILED
    org.opentest4j.AssertionFailedError: 
    expected: 2
     but was: 1
        at app//io.opentelemetry.sdk.metrics.export.PeriodicMetricReaderTest.shutdown_whileExportInFlight_waitsThenPerformsFinalExport(PeriodicMetricReaderTest.java:314)

PeriodicMetricReaderTest > shutdown_whileExportInFlight_waitsThenPerformsFinalExport() FAILED
    org.opentest4j.AssertionFailedError: 
    expected: 2
     but was: 1
        at app//io.opentelemetry.sdk.metrics.export.PeriodicMetricReaderTest.shutdown_whileExportInFlight_waitsThenPerformsFinalExport(PeriodicMetricReaderTest.java:314)

656 tests completed, 3 failed

https://github.com/open-telemetry/opentelemetry-java/actions/runs/24581486461/job/71880205316

cc @trask