build

Remove `--nworkers` #6367

Job	Run time
format-check	5m 42s
build-mdbook	8s
compiler-warnings	2m 56s
docker-tests	23m 24s
integration-tests (ubuntu-latest, oopsla19)	20m 35s
scaladoc-check	4m 10s
integration-tests (ubuntu-latest, arrays)	15m 14s
unit-tests (ubuntu-latest)	10m 30s
integration-tests (macos-latest, oopsla19)	32m 5s
unit-tests (macos-latest)	14m 44s
	2h 9m 28s

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