internal/pkg: exclusive artifacts

This alleviates scheduler overhead when curing many artifacts.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/ninja.go

@@ -7,7 +7,7 @@ func (t Toolchain) newNinja() pkg.Artifact {
 		version  = "1.13.2"
 		checksum = "ygKWMa0YV2lWKiFro5hnL-vcKbc_-RACZuPu0Io8qDvgQlZ0dxv7hPNSFkt4214v"
 	)
-	return t.New("ninja-"+version, []pkg.Artifact{
+	return t.New("ninja-"+version, false, []pkg.Artifact{
 		t.Load(CMake),
 		t.Load(Python),
 	}, nil, nil, `