ci(.radicle/ambient.yaml): add Radicle bin directory to path — radicle-ci-broker

I previously installed Radicle from a deb, which meant rad is in /usr/bin, and thus in the default $PATH. But now I install it with the Radicle installer, and need to add /root/.radicle/bin to $PATH.

Signed-off-by: Lars Wirzenius liw@liw.fi

       export CARGO_TARGET_DIR=/workspace/cache
       export CARGO_HOME=/workspace/deps
       export HOME=/root
       export PATH="/root/.cargo/bin:$PATH"
       export PATH="/root/.cargo/bin:/root/.radicle/bin:$PATH"
       # Check that `rad` is there.
       rad --help >/dev/null || (echo rad is not there; exit 1)
       cargo doc --workspace --no-deps