If one attempted to compile the test target for `radicle-node` by itself, it
would result in a compiler error – due to missing trait implementations that are
provided by `radicle-protocol/test`.
It would compile fine when `--all` is used due to cargo unifying feature sets,
so it went unnoticed until now.
This fixes the issue by adding `radicle-protocol` to the `dev-dependencies` and
enabling the `test` feature flag.
a8dac56ca6