Run Windows, Linux, and Mac CI tests with nightly and stable channels

.github/workflows/mac.yml

@@ -10,13 +10,16 @@ jobs:
     # https://help.github.com/en/actions/automating-your-workflow-with-github-actions/virtual-environments-for-github-hosted-runners#supported-runners-and-hardware-resources
     # macOS Catalina 10.15
     runs-on: macos-latest
-    name: (${{ matrix.target }}, nightly)
+    name: (${{ matrix.target }}, ${{ matrix.cfg_release_channel }})
+    env:
+      CFG_RELEASE_CHANNEL: ${{ matrix.cfg_release_channel }}
     strategy:
       fail-fast: false
       matrix:
         target: [
           x86_64-apple-darwin,
         ]
+        cfg_release_channel: [nightly, stable]
 
     steps:
     - name: checkout