[Test][C++] Fix flaky ReaderTest.testAsyncRead #1061

Job	Run time
Formatting Check	1m 39s
Run unit tests	0s
Lint	0s
Build the Wireshark dissector	0s
Build CPP Client on ${{ matrix.name }}	0s
Build ${{ matrix.pkg.name }} ${{ matrix.cpu.platform }}	0s
Build CPP Client on macOS with static dependencies	0s
Build with the C++20 standard	0s
Check Completion	0s
	1m 39s

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