HTTPClientTests.testRaceNewRequestsVsShutdown flaky (crash in `assert(self.pool.count == 0)`)

[weissi]

Failed in CI on 5.0 job https://ci.swiftserver.group/job/async-http-client-swift50-prb/884/console

Test Case 'HTTPClientTests.testRaceNewRequestsVsShutdown' started at 2021-05-27 13:09:25.562
Assertion failed: file /code/Sources/AsyncHTTPClient/HTTPClient.swift, line 117
Current stack trace:
0    libswiftCore.so                    0x00007f7d115b7830 _swift_stdlib_reportFatalErrorInFile + 115
1    libswiftCore.so                    0x00007f7d114f294c <unavailable> + 3463500
2    libswiftCore.so                    0x00007f7d114f2a3e <unavailable> + 3463742
3    libswiftCore.so                    0x00007f7d112ee189 <unavailable> + 1347977
4    libswiftCore.so                    0x00007f7d114c6a32 <unavailable> + 3283506
5    libswiftCore.so                    0x00007f7d112ed569 <unavailable> + 1344873
6    async-http-clientPackageTests.xctest 0x000055a276b5bc1b <unavailable> + 838683

this is distinct but probably related to #290 . The line in question is line 117 in HTTPClient.swift.

    deinit {
        assert(self.pool.count == 0)   <<<<<< THIS ONE
        assert(self.state == .shutDown, "Client not shut down before the deinit. Please call client.syncShutdown() when no longer needed.")
    }

[weissi]

CC @artemredkin / @fabianfett

[fabianfett]

https://ci.swiftserver.group/job/async-http-client-swift53-prb/215/console

[fabianfett]

Implementation replaced in #427. Not seen another instance of this in CI for now. If this comes up again it should be a new issue. (property count does not exist on connection pool anymore).