test: fix EventCollector double-free race in sse client tests #1917

Job	Run time
build-test-server-curl	8m 47s
build-test-server-mac-curl	7m 3s
contract-tests	4m 50s
contract-tests-curl	4m 55s
build-test-server	8m 44s
build-test-server-windows-curl	20m 2s
build-test-server-windows	16m 41s
build-test-server-mac	4m 29s
	1h 15m 31s

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