test: cover GetNumThreads default #2906

Job	Run time
lint / python-lint	5s
lint / clang-format	9s
ubuntu / ubuntu-gcc-build (ubuntu-24.04)	58s
ubuntu / ubuntu-gcc-build-debug (ubuntu-24.04)	1m 8s
ubuntu / ubuntu-gcc-build (ubuntu-24.04-arm)	3m 10s
mac / macos-clang-build	2m 6s
ubuntu / ubuntu-clang-build (ubuntu-24.04-arm)	2m 18s
ubuntu / ubuntu-clang-build (ubuntu-24.04)	1m 33s
windows / windows-msvc-build	2m 41s
mac / macos-clang-build-debug	2m 41s
windows / windows-clang-build	3m 12s
windows / windows-msvc-build-debug	5m 52s
mac / macos-clang-test	2m 22s
windows / windows-msvc-test	42s
windows / windows-clang-test	1m 0s
ubuntu / ubuntu-clang-test (ubuntu-24.04-arm)	1m 16s
ubuntu / ubuntu-clang-sanitizer-build (ubuntu-24.04)	2m 38s
ubuntu / ubuntu-clang-test (ubuntu-24.04)	1m 0s
windows / windows-msvc-test-extended	0s
windows / windows-clang-test-extended	0s
mac / macos-clang-test-extended	-1s
ubuntu / ubuntu-clang-test-extended	0s
ubuntu / ubuntu-gcc-test (ubuntu-24.04)	53s
ubuntu / ubuntu-gcc-test (ubuntu-24.04-arm)	1m 9s
ubuntu / ubuntu-clang-sanitizer-test (ubuntu-24.04)	2m 3s
ubuntu / ubuntu-gcc-test-extended	0s
ubuntu / ubuntu-gcc-build-codecov	0s
ubuntu / ubuntu-clang-sanitizer-test-extended	0s
perf	0s
	38m 55s

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