ci: actually test all feature combinations, add defmt.

the GHA `include` field is nonsense.

Author: Dirbaio

.github/workflows/test.yml

@@ -23,14 +23,18 @@ jobs:
           - x86_64-unknown-linux-gnu
           - thumbv6m-none-eabi
           - thumbv7m-none-eabi
+        features:
+          - ''
         include:
-          - target: x86_64-unknown-linux-gnu
+          - rust: stable
+            target: x86_64-unknown-linux-gnu
             features: std
-          - target: x86_64-unknown-linux-gnu
+          - rust: stable
+            target: x86_64-unknown-linux-gnu
             features: alloc
-          - target: x86_64-unknown-linux-gnu
-            features: std,tokio-1,futures-03
-            rust: nightly
+          - rust: nightly
+            target: x86_64-unknown-linux-gnu
+            features: std,tokio-1,futures-03,defmt-03
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@master