ci: fix problem building offline with Ambient

.radicle/ambient.yaml

@@ -8,15 +8,13 @@ plan:
 
   - action: shell
     shell: |
-      export CARGO_TARGET_DIR=/ci/cache
-      export CARGO_HOME=/ci/deps
       export HOME=/root
-      export PATH="/root/.cargo/bin:/root/.radicle/bin:$PATH"
+      export PATH="/root/.radicle/bin:$PATH"
 
       # Check that `rad` is there.
       rad --help >/dev/null || (echo rad is not there; exit 1)
 
-      cargo doc --workspace --no-deps
+      cargo doc --workspace --no-deps --locked --offline
 
       # FIXME: We can't run upgrade tests from older versions because
       # Ambient only fetches dependencies for the current version.