flaky-test: EventLoopTest.testMultipleShutdown

[PeterAdams-A]

03:04:46.619       2020-08-04 03:04:46.602 - Test Case '-[NIOTests.EventLoopTest testMultipleShutdown]' started.
03:04:46.619       2020-08-04 03:04:46.602 - Fatal error: leaking promise created at (file: "/otmp/od.5pDgAA/lw.RTsJDd/1v7v-68ck5pj0rtn6d_3-3541035/t.hz2yZS/0~5nYaaxKw8ZBxIxUfJqkrWyMJh4DCK6rYy18TXG3vHUqNR_bmwKLJhlYEJKABFXFH8No--MJEIOx2WZv654gTAA==/SRCROOT/Sources/NIO/EventLoop.swift", line: 484): file /otmp/od.5pDgAA/lw.RTsJDd/1v7v-68ck5pj0rtn6d_3-3541035/t.hz2yZS/0~5nYaaxKw8ZBxIxUfJqkrWyMJh4DCK6rYy18TXG3vHUqNR_bmwKLJhlYEJKABFXFH8No--MJEIOx2WZv654gTAA==/SRCROOT/Sources/NIO/EventLoop.swift, line 484
03:04:46.619       2020-08-04 03:04:46.602 - Exited with signal code 4

This was in an integration on swift 5.2