build mdbook as part of the PR CI #542

Job	Run time
Rustfmt	17s
Clippy	3m 37s
Code Coverage	9s
Tests (ubuntu-latest)	2m 5s
Build Wasm Examples (basic)	1m 6s
semver	51s
Build Wasm Examples (callback-example)	56s
Tests (macos-latest)	2m 24s
Build Examples (3d_charts)	31s
Build Examples (kaleido)	1m 21s
Build Examples (basic_charts)	35s
Build Book	1m 33s
Tests (windows-latest)	4m 42s
Build Examples (custom_controls)	25s
Build Examples (shapes)	34s
Build Examples (ndarray)	27s
Build Examples (maps)	47s
Build Examples (images)	45s
Build Examples (scientific_charts)	30s
Build Examples (subplots)	39s
Build Examples (financial_charts)	30s
	24m 44s

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