test: cover GetNumThreads default #2904

Job	Run time
lint / clang-format	8s
lint / python-lint	6s
mac / macos-clang-build-debug	1m 59s
mac / macos-clang-build	2m 7s
ubuntu / ubuntu-gcc-build (ubuntu-24.04-arm)	2m 49s
ubuntu / ubuntu-gcc-build (ubuntu-24.04)	1m 1s
ubuntu / ubuntu-clang-build (ubuntu-24.04-arm)	1m 49s
windows / windows-msvc-build-debug	5m 54s
ubuntu / ubuntu-clang-build (ubuntu-24.04)	1m 17s
ubuntu / ubuntu-gcc-build-debug (ubuntu-24.04)	1m 1s
windows / windows-clang-build	3m 52s
windows / windows-msvc-build	2m 30s
ubuntu / ubuntu-clang-sanitizer-build (ubuntu-24.04)	1m 19s
ubuntu / ubuntu-clang-test (ubuntu-24.04-arm)	1m 30s
ubuntu / ubuntu-clang-test (ubuntu-24.04)	1m 13s
mac / macos-clang-test	1m 21s
ubuntu / ubuntu-gcc-test (ubuntu-24.04-arm)	47s
ubuntu / ubuntu-gcc-test (ubuntu-24.04)	41s
windows / windows-msvc-test	43s
windows / windows-clang-test	51s
mac / macos-clang-test-extended	-1s
windows / windows-msvc-test-extended	-1s
windows / windows-clang-test-extended	-1s
ubuntu / ubuntu-clang-sanitizer-test (ubuntu-24.04)	56s
ubuntu / ubuntu-gcc-test-extended	0s
ubuntu / ubuntu-clang-test-extended	0s
ubuntu / ubuntu-gcc-build-codecov	0s
ubuntu / ubuntu-clang-sanitizer-test-extended	0s
perf	0s
	33m 51s

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