ci: split x86 pytests by directory #1563

Job	Run time
select-runner	1s
build (3.7, x64, ubuntu)	12m 54s
build (3.7, x64, windows)	8m 11s
build (3.11, x64, ubuntu)	12m 54s
build (3.11, x64, macos)	4m 46s
build (3.11, x64, windows)	12m 48s
build (3.9, macos, --cov=psyneulink)	3m 39s
build (3.9, ubuntu, --forked -m "not llvm")	7m 22s
build (3.8, x86, windows)	7m 15s
build (3.10, ubuntu, --fp-precision=fp32)	12m 56s
build (3.10, macos, -m benchmark --benchmark-enable --benchmark-only --benchmark-min-rounds=2 --b...	5m 40s
build (3.7, x64, ubuntu, min)	12m 56s
build (3.8, x64, macos)	4m 30s
	1h 45m 52s

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