ci: add ring build to test phase

Previously we did not have a test step that would run the unit tests
assuming the equivalent of default features, but with the default
crypto provider (now `aws-lc-rs`) with the alternative built-in option
(now `ring`).

.github/workflows/build.yml

@@ -66,6 +66,11 @@ jobs:
         env:
           RUST_BACKTRACE: 1
 
+      - name: cargo test (debug; defaults+ring)
+        run: cargo test --no-default-features --features ring,native-tokio,http1,tls12,logging
+        env:
+          RUST_BACKTRACE: 1
+
       - name: cargo test (debug; all features)
         run: cargo test --all-features
         env: