test: cover GetNumThreads default #2910

Job	Run time
lint / clang-format	10s
lint / python-lint	5s
mac / macos-clang-build-debug	1m 52s
mac / macos-clang-build	2m 11s
ubuntu / ubuntu-gcc-build-debug (ubuntu-24.04)	1m 18s
ubuntu / ubuntu-gcc-build (ubuntu-24.04)	1m 25s
ubuntu / ubuntu-gcc-build (ubuntu-24.04-arm)	3m 29s
ubuntu / ubuntu-clang-build (ubuntu-24.04)	1m 16s
ubuntu / ubuntu-clang-build (ubuntu-24.04-arm)	2m 19s
windows / windows-msvc-build-debug	5m 35s
windows / windows-msvc-build	2m 32s
windows / windows-clang-build	3m 16s
mac / macos-clang-test	1m 23s
ubuntu / ubuntu-clang-sanitizer-build (ubuntu-24.04)	1m 22s
ubuntu / ubuntu-clang-test (ubuntu-24.04-arm)	1m 21s
ubuntu / ubuntu-clang-test (ubuntu-24.04)	1m 2s
windows / windows-msvc-test	49s
ubuntu / ubuntu-gcc-test (ubuntu-24.04)	41s
ubuntu / ubuntu-gcc-test (ubuntu-24.04-arm)	55s
windows / windows-msvc-test-extended	0s
mac / macos-clang-test-extended	-1s
ubuntu / ubuntu-clang-test-extended	0s
ubuntu / ubuntu-clang-sanitizer-test (ubuntu-24.04)	59s
ubuntu / ubuntu-gcc-test-extended	0s
ubuntu / ubuntu-gcc-build-codecov	0s
windows / windows-clang-test	53s
ubuntu / ubuntu-clang-sanitizer-test-extended	-1s
windows / windows-clang-test-extended	0s
perf	0s
	34m 51s

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