Also validate crates build without default features

Note that tests can't work without default features as they assume
them to exist, and we have to chose one, going for the one most
users will see.

.github/workflows/rust.yml

@@ -19,6 +19,7 @@ jobs:
           source ~/.profile
           make test-gen
           make gen-all-cli cargo-api ARGS=test
+          make cargo-api ARGS='check --no-default-features'
           make cargo-api ARGS=doc
           make docs-all
           cargo test