Add spellcheck to CI #4280

Job	Run time
deno-checks	9s
all-features (ubuntu-20.04)	5m 50s
oldstable (ubuntu-20.04)	2m 20s
all-features (macos-14)	5m 11s
oldstable (macos-14)	2m 16s
clippy (ubuntu-20.04, --all-features)	2m 34s
oldstable (windows-latest)	5m 20s
rustfmt	10s
clippy (macos-14, --all-features)	2m 31s
clippy (windows-latest, --no-default-features -F extensions)	8m 23s
shellcheck	5s
spellcheck	1m 9s
test-matrix (ubuntu-20.04)	5m 30s
test-matrix (macos-14)	5m 13s
test-matrix (windows-latest, --no-default-features -F extensions)	12m 6s
test	1s
	58m 48s

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