[infra] Use Pub Workspaces #1176

Job	Run time
build (ubuntu, stable, native_assets_builder, false)	5m 20s
build (ubuntu, stable, native_assets_cli, false)	2m 22s
build (ubuntu, stable, native_toolchain_c, false)	2m 27s
build (ubuntu, main, native_assets_builder, false)	5m 22s
build (ubuntu, main, native_assets_cli, false)	23m 38s
build (ubuntu, main, native_toolchain_c, false)	2m 34s
build (macos, stable, native_assets_builder, false)	4m 40s
build (macos, stable, native_assets_cli, false)	1m 47s
build (macos, stable, native_toolchain_c, false)	2m 4s
build (macos, main, native_assets_builder, false)	5m 17s
build (macos, main, native_assets_cli, false)	1m 42s
build (macos, main, native_toolchain_c, false)	2m 17s
build (windows, stable, native_assets_builder, false)	9m 18s
build (windows, stable, native_assets_cli, false)	3m 17s
build (windows, stable, native_toolchain_c, false)	5m 46s
build (windows, main, native_assets_builder, false)	9m 18s
build (windows, main, native_assets_cli, false)	4m 24s
build (windows, main, native_toolchain_c, false)	4m 57s
coverage-finished	0s
	1h 36m 30s

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