Use prebuilt try-runtime binary in CI (#1898)

`cargo install` takes a long time in CI. We want to run it relatively
frequently without chewing through so much compute (see
https://github.com/paritytech/ci_cd/issues/771) so I added automatic
binary releases to the try-runtime-cli repo.

A small added benefit is we can use it in our existing
`on-runtime-upgrade` checks, which should cut their execution time by
about half.