CI: Add some flags.

.github/workflows/ci.yml

@@ -26,14 +26,20 @@ jobs:
 
   coverage:
     name: Test Coverage
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
+    env:
+      OS: ${{ matrix.os }}
     steps:
       - name: Checkout Repository
         uses: actions/checkout@v4
       - name: Install Rust Toolchain
+        id: toolchain
         uses: dtolnay/rust-toolchain@v1
         with:
-          toolchain: 1.63
+          toolchain: stable
           components: llvm-tools-preview
       - name: Install cargo-llvm-cov
         uses: taiki-e/install-action@cargo-llvm-cov
@@ -43,8 +49,9 @@ jobs:
         uses: codecov/codecov-action@v3
         with:
           file: lcov.info
-          flags: unittests
+          flags: unittests,${{ steps.toolchain.outputs.name }}
           name: iof
+          env_vars: OS
           # Failing to upload results will cause a CI error.
           # So remember to use a token.
           fail_ci_if_error: true