qa: Limit `-maxconnections` in tests #3845

Job	Run time
ASan + LSan + UBSan + integer, no depends, USDT	1h 9m 37s
macOS 14 native, arm64, no depends, sqlite only, gui	18m 50s
macOS 14 native, arm64, fuzz	12m 24s
test each commit	0s
Win64 native, VS 2022	1h 52m 34s
Win64 native fuzz, VS 2022	42m 46s
	4h 16m 11s

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