.github/workflows: Add emulated tests for riscv64 and s390x. #1703

Job	Run time
Run tests (emulated riscv64)	9s
Run tests (emulated s390x)	3s
Run benchmarks	1m 10s
Run checks	29s
Check relative links in website	10s
Run tests (ubuntu, 1.22.x)	1m 26s
Run tests (macos, 1.22.x)	1m 7s
Upload SourceGraph LSIF	28s
Run tests (windows, 1.22.x)	2m 33s
Run tests (ubuntu, 1.21.x)	21s
Upload test coverage (linux)	6s
Upload test coverage (macos)	7s
Upload test coverage (windows)	7s
	8m 16s

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