[CI] exit with code 1 when fail

This MR makes sclang exit with code 1 when there have been failures in running our unit tests.

As you can see, one of the tests currently fails (for a very trivial reason) and the CI pipeline indicates a failure. I'll fix the failing test in another MR asap.

Also, this MR pins our dependency on NodeSnapshot to version 0.2.0. This is a temporary fix that will keep our CI from constantly failing while we work on a longer term solution.