Apparently GitLab CI defaults to declaring all jobs of the previous
stage as dependencies of a job. This meant that we would end up
downloading all of our binary distributions during the `cleanup` stage,
eating up a truly remarkable amount of S3 tranfers.

See #16085.

It's pretty unlikely we will be going back to circleci at this point

[skip-ci]

Although the Haddock's for `shiftL` and `shiftR` do require the number
of bits to be non-negative, we should still check this before calling
out to primitives (which also have undefined behaviour for negative bit
shifts).

If a user _really_ wants to bypass checks that the number of bits is
sensible, they already have the aptly-named `unsafeShiftL`/`unsafeShiftR`
at their disposal.

See #16111.