Fix contributing md link in building.md #1753

Job	Run time
Run benchmarks	1m 38s
Run tests (emulated riscv64)	1m 21s
Run tests (emulated s390x)	1m 34s
Run tests (ubuntu, 1.23.x)	1m 44s
Run tests (macos, 1.23.x)	1m 40s
Check relative links in website	19s
Run tests (windows, 1.23.x)	2m 56s
Run tests (ubuntu, 1.22.x)	1m 12s
Run checks	1m 1s
Upload test coverage (linux)	13s
Upload test coverage (macos)	13s
Upload test coverage (windows)	12s
	14m 3s

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