Add `OsSystem` support to mdtests (#16518) #41583

# to view logs

Job	Run time
cargo build (release)	7m 52s
cargo fmt	20s
Determine changes	12s
mkdocs	2m 48s
pre-commit	3m 24s
python package	1m 41s
cargo clippy	1m 55s
benchmarks	4m 32s
cargo build (msrv)	2m 2s
cargo fuzz build	3m 59s
cargo shear	21s
cargo test (linux)	2m 2s
cargo test (linux, release)	4m 14s
cargo test (wasm)	1m 43s
cargo test (windows)	4m 39s
formatter instabilities and black similarity	3m 25s
test scripts	1m 12s
test ruff-lsp	31s
fuzz parser	5m 49s
ecosystem	0s
	52m 41s

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