Fix flaky test TransactionTests.testCancelAsyncRequest

[dnadoba]

Resolves #706.
The continuation is resumed with the cancelation error before we cancel the scheduled request.

async-http-client/Sources/AsyncHTTPClient/AsyncAwait/Transaction.swift

Lines 290 to 294 in 62c06d4

	case .failResponseHead(let continuation, let error, let scheduler, let executor, let bodyStreamContinuation):
	continuation.resume(throwing: error)
	bodyStreamContinuation?.resume(throwing: error)
	scheduler?.cancelRequest(self) // NOTE: scheduler and executor are exclusive here
	executor?.cancelRequest(self)

Therefore this test is inherently flaky. The fix waits up to one second for the scheduled request to be canceled.

[dnadoba]

5.6 fails with

[505/505] Testing AsyncHTTPClientTests.NoBytesSentOverBodyLimitTests/testNoBytesSentOverBodyLimit

Test Suite 'Selected tests' started at 2023-08-14 19:20:37.322
Test Suite 'TransactionTests' started at 2023-08-14 19:20:37.325
Test Case 'TransactionTests.testCancelAsyncRequest' started at 2023-08-14 19:20:37.325

Exited with signal code 4
1
Build step 'Execute shell' marked build as failure

not sure what is happening.

[yim-lee]

CI cleanup might have caused the doc check failure? @swift-server-bot test this please