Speed up CI a bit: run only component-model tests under component-model feature. (#4221)

Right now the CI test job runs `cargo test --features component-model`
and runs all tests with this feature enabled, which takes a bit of time,
especially on our emulation-based targets. This seems to have become the
critical path, at least in some CI jobs I've been watching. This PR
restricts these runs to only component-model-specific tests when the
feature is enabled.

.github/workflows/main.yml

@@ -300,7 +300,7 @@ jobs:
 
     # Test the component-model related functionality which is gated behind a
     # compile-time feature
-    - run: cargo test --features component-model
+    - run: cargo test --test all --features component-model component_model
 
   # Build and test the wasi-nn module.
   test_wasi_nn: