experiment with explicit thread number #7007

Job	Run time
Lints and doc tests on ubuntu-latest	7m 3s
Unit tests on ubuntu-latest	19m 0s
Lints and doc tests on windows-latest	16m 3s
Unit tests on windows-latest	7m 52s
Lints and doc tests on macos-13	12m 41s
Unit tests on macos-13	12m 10s
Lints and doc tests on macos-14	8m 3s
Unit tests on macos-14	15m 3s
Memory leak checks	2m 19s
CI status checks	1s
	1h 40m 15s

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